Perception Across the Senses

Perception Across the Senses


The perception of the environment does not occur within a single sense.  The world is perceived through interactions between the senses integrated and cueing the other senses (Fairhall & Macaluso, 2009).  These interactions between the auditory, visual, and tactile sensory systems have been a field of rampant growth within the field of cognition in the last couple of decades.  Indeed, a few decades earlier, the interaction between modalities would have been viewed as somewhat exotic. (Spence, 2004)  How the brain represents space is of a particular interest to modern psychology, has been used in the creation of multitudes of new technologies, and is integral to the understanding of consciousness.  Of particular relevance to the studies of the brain’s construction of space is attention; therefore, the properties of attention must also be examined in detail to explain how the attention is modulated between the sensory modalities.  Multisensory attention can be viewed as a way that human beings control their senses to perceive the world.

The senses are linked together, in a regulatory process that allows for attention to pass through multiple modalities, while simultaneously drawing information from each one.  These cross-modal links among vision, touch, and audition have been tested to reveal an underlying cortical system devoted to multisensory integration  (Kida, 2009).  The brain seems to use the senses in concert, with each sense able to activate or primes the other senses and integrate sensory information from multiple modalities (Fairhall and Macaluso, 2009) This paper will examine many of the underlying mechanisms of multisensory integration, as well as the base senses themselves, especially vision.  The properties of attention must also be examined to understand multisensory attentions; therefore an in depth review of the properties of attention is a necessary first step to understand how the different senses communicate to create a complete and seamless conscious stream.  

Properties of Attention

            Attention and its various principles are some of the most researched principles of psychology, especially cognitive psychology.  Attention is required in almost any conscious process, and some have indeed equated attention with consciousness itself.  The properties of this locus of sensation interpreted into conscious perception and further reactive capabilities have many aspects yet to be resolved. (Lavie, 1995)  One controversial subject within the field of attention studies is the late attention model versus the early selection model.  This is an argument that focuses on where the “bottleneck” of attention is.  This is the study of the limits of attention and how its capacity is limited.  The early and late selection models were created to explain why irrelevant stimuli are perceived and why certain stimuli will be perceived whereas others will not.   In 1995, Lavie took these two approaches to attention and combined them into a hybrid theory of selective attention based on load and task difficulty.  This effectively combined the two concurrent models of attention and provides us with a consistent and well-based beginning of an approach to the modulation of attention resources by the perceptual systems.

            Lavie’s theories of attention should be examined in more detail so that the study of uni-modal and cross-modal sensory integration and attention can be more completely understood.  One problem that is not solved by this approach is the ability to perceive certain information even under high load conditions (Lavie, 2010).  It seems as though the properties of attention are also specific and subjective for each individual and therefore are very hard to study comprehensively.  But the hybrid model has solved many of the internal disputes of the two opposing views of late and early attention models by allowing for the limited capacity of attention and the assumption that perception is somewhat automatic, allowing for the limited capacity of attention and the assumption that perception is somewhat automatic cannot consciously shut it shut down (Lavie, 2010).  According to Lavie, the locus of attention shifts with the difficulty of the task, with easier tasks allowing more irrelevant stimuli to be perceived than more difficult tasks, which would mean a constantly shifting “filter” that has a threshold and limitations on what can be perceived.

            The shifting locus of attention seems to be viewed as somewhat of a filter for irrelevant stimuli while simultaneously having a built in “alarm system” that responds quickly to important stimuli.  This filter has been the subject of the majority of Lavie’s studies because of her studies on task difficulty and the effective limitations that attention has to be able to capture or receive stimulus input.  It has been shown that even the perception of biological stimuli like optic flow is reduced by demanding yet separate tasks. (Lavie, 1997)  This would lead to the belief that the resources of attention are inter-modal, and distributed between the senses based on what can be perceived by each modality.  The information is then integrated across multiple levels in various different parts of cortex.  This multisensory integration between the three primary senses of touch, audition, and vision is the next step in the study of cross-modal attention.

Multisensory Integration 

            Multisensory integration is necessary to recognize different inputs from sensory modalities as pertaining to the same object (Koelewijn, 2010) Results have even demonstrated that during multisensory integration, the brain combines inputs not only from sensory modalities, but acts upon these inputs in concert with the peripheral nervous system to allow for perceptual enhancements (Lugo, Doti, Wittich, & Faubert, 2008).  However, this multisensory integration is not the same thing as attention, even though many studies have shown correlations between the two.  Some studies have suggested that multisensory integration is preattentive and immune to top-down influences (Fairhall & Macaluso, 2009).  However, it is probable that the integration and cortical communication between modalities is not comprehensively understood, which is the position many researchers have taken on the issue.

Integration of multisensory inputs occurs when different senses are detecting the same stimulus at about the same time, at about the same location.  One example of this as an illusion is ventriloquism, which tricks vision into integrating movement information with a sound produced in a slightly different (but unnoticeable) location.  Because the movement takes place simultaneously with lip movement from the puppet, the sound is perceived as emanating from the puppet. Shams, Kamitani, and Shimojo developed another illusory effect that proves that audition biases the visual system in 2000.  They showed that multiple short auditory beeps transformed the visual perception of an event into multiple flashes.  These examples of illusory events show that the multisensory integration systems can be fooled, now they systems themselves must be examined in detail to understand how the senses work across modalities in unison to control attention.

            Multisensory integration can enhance visual search enhance the salience of objects (Koelewijn, 2010).  When a short sound is shown simultaneously with a color change of a target stimulus, the stimulus seems to become separate from the display proving that visual search is enhanced by audition (Koelewijn, 2010).  What these experiments show is the strength of the multisensory integration system to bias, enhance, or facilitate the other senses.  It is a kind of additive process that increases the perceiver’s ability to discriminate, search, and react to the surrounding environment.  However, there are constraints to how the senses can integrate, namely temporal and spatial limitations.

            It is believed that the multisensory integration sites converge unimodal information into unimodal or multimodal sites.  This is believed to only occur with certain constraints pertaining to the location and time between stimulus presentations.  There is also believed to be a rule of inverse effectiveness, which states that the multisensory integration effect is larger with less perceptually powerful stimuli, or less salient stimuli.  The temporal and locational constraints upon the multisensory integration system have been the study of previous research and the constraints upon the multisensory systems are relatively well known.  The results of the studies have shown that there is about a 100-millisecond time window in which the stimuli must be presented, or the multisensory integration will be significantly reduced.  This provides a fairly clear difference from preparatory states, or cueing and alerting of the different sensory systems (Koelewijn, 2010).  

The location of the stimulus is also very important for integration to occur.  However, these spatial constraints seem to be limited to the periphery; if the target is within the region of the fovea multisensory integration will almost certainly occur.  Auditory sounds will enhance the visual perception of objects if the sound is only temporally relevant and the visual stimulus is at the center of fixation.  This implies that sound works in concert with vision in the periphery to enhance the salience of objects, but in the center of the visual field the object will always be enhanced by simultaneous multimodal stimuli.  This infers that multimodal integration occurs at many cortical sites and is indeed shown to do so by many researchers.

            The cortical sites know to integrate multisensory events are not modal specific.  The primary visual cortex integrates auditory information just as there are sites specific for multisensory integration.  The primary brain regions involved in multisensory integration are the superior temporal sulcus and gyrus, the ventral and lateral intraparietal areas, and sub cortical areas such as the superior colliculus (Koelewijn, 2010).  However, the typically unimodal sites are also involved in the processes of multisensory integration, such as the primary visual cortex and primary visual cortex. The superior temporal sulcus is primarily involved in audiovisual integration and is one of the most highly studied cortical areas involved with multisensory integration.  However, it is believed that all of these areas communicate using feed forward connections and polysynaptic feedback loops, creating an additive integration process that increases in effectiveness as the stimuli decrease in intensity (Fairhall & Macaluso, 2009).

            The audiovisual integration effect is one of the more studied and probably the most often used of the multimodal integration effects.  We use this when attending to the visible speech patterns of another person.  The superior temporal sulcus is the brain area shown to integrate speech and visual patterns of movement.  A direct integration effect exists between vocal tract shape, speech acoustics, and deformation of the face, which can signal the starting and stopping of words, sentences, and ideas.  The biological motion of the mouth, neck, and head provide enormous amounts of information for the sound information that is going to be received.  Indeed, the activity of the superior temporal sulcus is super additive with congruent stimuli, as are the primary visual and auditory cortices.  (Callan, D.E.,Jones, Munhall, Kroos, Callan, A.M., & Bateson, 2004).

            Another brain area that has important implications for audiovisual integration is the superior colliculi, which is known as a brain area that reorients visual gaze, especially in saccadic eye movements.  The colliculus’ ability to reorient gaze to peripheral events shows that the brain integrates multisensory information in many cortical areas that are also devoted largely to one mode of perception.  The superior colliculus is known to reorient gaze to a visual movement with a saccade, but also receives input from other modalities, making it a polymodal integration site (Nelson, Hughes, & Aronchick, 1997) The summation, or additive effects of the multimodal inputs to the superior colliculus was observed by Nelson and Hughes’ study, confirming both the spatial constraints of multimodal integration and the role of the superior colliculus in multimodal perception.  Multimodal integration has been studied effectively over the last decade, but the ability for imaging of the brain has greatly increased during this time, so an fMRI study would greatly increase the knowledge of how audiovisual stimuli are integrated in the cortex.

            Moving back to the superior temporal sulcus, it has been shown that voxels of fMRI data show interactions of audio and visual inputs have a mixture of unisensory and multisensory subpopulations, some with uniquely unisensory inputs and some with uniquely multisensory inputs, whose subpopulations were not visible until high resolution fMRI was used to image the activations in cortex (Attenveldt, Blau, Blomert, & Gloebel, 2010).  This means that there are certain areas of cortex completely devoted to multisensory integration, as well as sites that process both a singular modality and multiple modalities, such as the primary visual or auditory cortex.  Pertaining to this research of intermodal connections within brain sites is the brain activity of the blind and deaf in terms of the plasticity of the brain.

            It seems that the brain can compensate for lacking in one type of modality. fMRI data has shown that cross-modal plasticity occurs predominantly in the right auditory cortex for the deaf.  Studies have shown that the auditory cortex in the deaf has visual activation in response to lip movements that are normally used for auditory processing in hearing patients (Finney, Fine, & Dobkins).  Therefore, the right auditory cortex of the deaf, because there is no auditory input received by the cortex, might be able to process motion in the visual modality.  But perhaps the most important aspect of this finding is the reciprocal findings in blind subjects.  In many blind patients, moving auditory stimuli have been observed to activate the right visual cortex.  This occurs again in the right hemisphere of cortex leading to the possibility that plasticity for motion processing in that hemisphere, as well as supporting the right visual cortex’s predisposition towards motion processing (Finney, Fine, & Dobkins).  This neuroplasticity supports the idea of an integrated and connected system of sensory processing that works in parallel to create a conscious perception of the world, especially between the two modalities of vision and audition.  There is even more evidence of such plasticity in the multisensory dorsal stream functioning.

            Localizing objects and navigating motor functions in the environment have been shown to be a part of the dorsal visual stream of information that receives input from the early visual areas (primary visual cortex) and projecting to the posterior parietal cortex Fiehler & Rosler, 2010).  The posterior parietal cortex works is believed to work as an integrator for multiple senses that guides movement in space and can even provide a unified representation of space.  It seems that this dorsal pathway is highly used by the brain to process how to use motor movements to correctly interact with the environment, whereas the ventral stream would be implied for the accurate perception of the object, such as size or distance.  In Fiehler and Rosler’s (2010) study, evidence for the polymodal integration system in the dorsal stream was found that parallels the ideas of multisensory integration already discuss.  This study provides another example of the everyday usage of multisensory information and obvious and necessarily useful integration of the tactile and visual modalities. 

So far, we have examined various aspects of the integrator systems of the senses, the various properties of attention, and how many of the primary sensory areas of cortex are multimodal.  This is but a brief examination of the subject matter, the knowledge and complexity of this field is extraordinarily complex and intricate with large amounts of information on the integration of information within the brain.  There is much research left to be done in the fields of attention and the integration of the senses, but this review should provide a basic overview of the knowledge obtained thus far in the two fields discussed.  However, to fully understand how the senses work in unison, we must step out of the constraints of multisensory integration and the basic tenets of attention into the realm of cross-modal attention.

Cross-modal Attention

Construction, maintenance, and updating of the cognitive representations of space surrounding an organism are essentially for higher functioning and adaption to the environment and the combination of cues of sensory data from the different modalities is often the best way to achieve an adaptive, representative perception of the environment (Spence, 2005).  The fields of multisensory integration and cross-modal attention are highly overlapping; however, it would seem that the main difference between the two fields of research is temporal.  Indeed, cross-modal attention necessarily implies the use of attentive resources, whereas multisensory integration does not necessarily.  This may be due to modern scientific techniques of testing reaction times and cueing, because the differences between the two ideas are minimal and possibly fabricated due to the constraints of laboratory settings.  It is possible that in the real world, such a dichotomy does not exist, which is the view I put forward.  However, for the sake of maintaining consistency with the research in the field, I have provided a dichotomy for the two. 

The difference between multisensory integration and cross-modal attention as defined by Koelewijin (2010) is that multisensory integration is preattentive, occurring at many different levels, whereas cross modal attention has to do with the focusing of the resources of attention.  Multisensory integration only occurs when the cue in one modality and target of a different modality are close together and nearly simultaneous.  Cross-modal cueing effects occur when the cue precedes the target by at least some time, between about fifty and three hundred milliseconds (Spence, 2010). But as discussed earlier, multisensory integration takes place between zero and one hundred milliseconds; therefore, multisensory integration and cross modal attention overlap. 

Cross modal attention has been the subject of a large body of research over the past couple decades.  Spence claims in his research (2004) that the interaction between the senses is the essence of the perceptual construction of the environment.  There is indeed good evidence for a neural system underlying cross-modal links (Kida, Inui, Tanaka, & Kakigi, 2010).  fMRI studies have shown that the intraparietal sulcus and the temporoparietal junction is activated in spatial cueing tasks, and TMS (transcranial magenetic imaging) has also provided support for the intraparietal region (Kida, Inui, Tanaka, & Kakigi, 2010).  However, just as multisensory integration was shown to affect the primary receivers for unimodal sensations, these areas are also responsive to cueing from different modalities.  This means that attention is not only involved with the processing of the primary modality, but also the modality specific brain areas in an irrelevant modality (Nager, Estorf, & Munte, 2006).  There does seem to be one area of cortex that is devoted to modulating the field of attention that is not dependent upon a modality.  This is referred to as the supramodal effect of cross modal attention, and it still highly debatable in the field of cognitive neuroscience.

Supramodal Model of attention

            The supramodal model of attention is a theory that insists that there is a common neural pathway that can control the spatial shifts of the field of attention within and between different modalities (Macaluso, Frith, & Driver).  Driver and Frith (2000) also found that both vision and touch share a supramodal effect for vision and touch in the intraparietal sulcus.  There has also been evidence that the right hemisphere controls for the shifting and general allocation of attention to different modalities, but this is not absolute, because both hemispheres show activation for crossmodal attention tasks.  The inferior premotor cortex was also found to be active during crossmodal tasks, giving reasons to believe that attention primes the motor cortex to react to the environment (Macaluso, Frith, & Driver).  Many studies have also found that the superior premotor cortex and superior temporo-parietal junction were active during visual attention tasks, showing that they are possibly responsible for major shifts of attention.  This shifting of attention between the senses is not automatic, as many researchers had thought prior to 2007.

            Experiments have shown that the crossmodal cueing effects are eliminated under conditions where the participants have to attend to high load tasks in a single modality (Spence, 2010).  This is consistent with Lavie’s load theory and helps to expand the limitations of attention across modalities.  It seems that tactile cueing as a whole can be eliminated when the participant monitors a rapid series visual stream, meaning that crossmodal attention is not automatic.


Beauchamp, M. S., Argall, B. D., Bodurka, J., Duyn, J. H., & Martin, A. (2004). Unraveling multisensory integration: patchy organization within human STS multisensory cortex. Nature Neuroscience, 7, 1190-1192.

Callan, D. E., Jones, J. A., Munhall, K., Kroos, C., Callan, A. M., & Vatikiotis-Bateson, E. (2004). Multisensory Integration Sites Identified by Perception of Spatial Wavelet Filtered Visual Speech Gesture Information. Journal of Cognitive Neuroscience, 16, 805-816.

Fairhall, S. L., & Macaluso, E. E. (2009). Spatial attention can modulate audiovisual integration at multiple cortical and subcortical sites. European Journal of Neuroscience, 29, 1247-1257.

Fiehler, K., & Rösler, F. (2010). Plasticity of multisensory dorsal stream functions: Evidence from congenitally blind and sighted adults. Restorative Neurology & Neuroscience, 28(2), 193-205. 

Finney, E. M., Fine, I., & Dobkins, K. R. (2001). Visual stimuli activate auditory cortex in the deaf. Nature Neuroscience, 4, 1171.

Hughes, H., Nelson, M., & Aronchick, D. (1998). Spatial characteristics of visual- auditory summation in human saccades. Vision Research, 38, 3955-3963.

Kida, T., Inui, K., Tanaka, E., & Kakigi, R. (2011). Dynamics of within-, inter-, and cross-modal attentional modulation. Journal Of Neurophysiology, 105(2), 674-686.

Lavie, N. (1995). Perceptual load as a necessary condition for selective attention. Journal of Experimental Psychology: Human Perception and Performance, 21, 451-468.

Lavie, N. (2010). Attention, distraction, and cognitive control under load. Current Directions in Psychological Science, 19, 143-148.

Lavie, N., Hirst, A., de Fockert, J. W., & Viding, E. (2004). Load Theory of Selective Attention and Cognitive Control. Journal of Experimental Psychology: General, 133, 339-354

Lavie, N. (2005). Distracted and confused?: Selective attention under load. Trends in Cognitive Sciences, 9, 75-82

Lugo, J. E., Doti, R. R., Wittich, W., & Faubert, J. (2008). Multisensory integration: Central processing modifies peripheral systems. Psychological Science, 19, 989-997.

Macaluso, E. E., Frith, C. D., & Driver, J. J. (2002). Supramodal Effects of Covert Spatial Orienting Triggered by Visual or Tactile Events. Journal of Cognitive Neuroscience, 14(3), 389-401. 

Nager, W., Estorf, K., & Münte, T. F. (2006). Crossmodal attention effects on brain responses to different stimulus classes. BMC Neuroscience, 731-738.

Rees, G., Frith, C. D., & Lavie, N. (1997). Modulating irrelevant motion perception by varying attentional load in an unrelated task. Science, 278, 1616-1619.

Sotto-Faraco, S. (2005). Book review. European Journal of Cognitive Psychology, 17(6), 882-885. 

Spence, C. (2010). Crossmodal spatial attention. Annals Of The New York Academy Of Sciences, 119, 1182-200.

Spence, C., & Parise, C. (2010). Prior-entry: a review. Consciousness and Cognition, 19(1), 364-379. 

Van Atteveldt, N. M., Blau, V. C., Blomert, L., & Goebel, R. (2010). fMR-adaptation indicates selectivity to audiovisual content congruency in distributed clusters in human superior temporal cortex. BMC Neuroscience.

The Different States of Consciousness and the Constructive Processes Associated with Human Cognition

The concept of consciousness is extremely elusive, there are no concrete operation definitions and despite the enormous amounts of research on the subject throughout history.  Many aspects of what would be considered conscious perception are constructive; the mind seems to create parts of the environment, just as it perceives the environment.  These constructive processes of the mind are evoked when we dream, during hallucinations whether drug induced or resulting from a psychosis or neuropsychological disorder, and during conscious awareness.  Much can be ascertained about the constructive nature of consciousness from these realms of subjective experience.  Indeed, these three areas of psychology are historically controversial, giving even more weight to a review of their processes in light of the overall tenets of conscious perception.  These areas apply primarily to perception in the visual modality; therefore, the tenets of vision will be a large aspect of the discussion of the creative nature of consciousness.  These facets are but limited sources of information about constructive conscious perception, and the puzzle of consciousness has many pieces to be yet completed. 


REM Sleep and Dreaming

Dreaming is perhaps the most important of the constructive processes that can be used to study the constructive nature of consciousness.  Historically, it has been misunderstood and misinterpreted as symbolic representation of repression within the psyche, as a portal to an alternate dimension, and even as a predictor of future events.  Many viewpoints have been taken on the nature of dreams; however, this process is far different than most early researchers could have realized.  With new technological advances in the realms of neuropsychology, we can uncover some of the basic physiology of REM sleep, in which the majority of dreaming occurs.  Another aspect of dreaming and REM sleep that provide information upon the constructive nature of the mind are the multitudes of sleep disorders and large amounts of clinical research done on the nature of sleep. However, the subject of the importance of dreams is still under debate.  Dreams are constituted of sensations and emotional content, usually perceived as real by the dreamer (Dang-Vu, et al., 2005).  Most dreams are weird, non-linear narratives that are instable in terms of time, places, and people, and are most often forgotten upon waking.  Most of the information that will be used to discuss the tenets of consciousness can be viewed in terms of dreams; hallucinogens and neuropsychological disorders are most aptly depicted as being within a dream, due to the disorganization and erratic functioning of the mind during these conditions.  Dreaming is the first step into the realm of the mind’s active constructive of the environment.  Since dreaming occurs primarily in REM sleep, the physiology of REM sleep is intrinsic to the understanding of dreams.

REM sleep is a highly complex phenomenon.  It is most often associated with vivid dreams and high levels of brain activity (McCarley, 2011).  The first cycle of REM sleep usually takes place around 70 minutes after falling asleep and is defined by fast, low-voltage EEG activity, the suppression of motor movement, and the occurrence of rapid eye movements (McCarley, 2011).  The first REM period of sleep tends to be shorter, with increasingly larger amounts of REM as the sleep cycle persists throughout the night and delta waves (deep sleep) diminish.  REM sleep is present in all mammals and some birds (McCarley, 2011).   This insists of an evolutionary importance of REM sleep, which is the view put forward by this paper.  The size of the animal also seems to be correlated to the necessity of REM sleep, because elephants have the longest cycles of REM stage sleep.  In the uterus, mammals spend approximately 50 to 80% of their time in REM sleep, and animals born prematurely have much higher rates of REM sleep (McCarley, 2011).  As development continues, the percentage of REM sleep declines.  The facts highly support the necessity of REM sleep for nervous system development and many scientists believe that it can predict synaptic density.  REM sleep facilitates brain development by increasing the amount of nervous tissue and promoting the psyiological maturity of the existing tissue (Chiş, 2009). 

The physiology of REM sleep would infer that this process is completely necessary for what can be described as consciousness, because the definition of conscious beings seems to be limited to the groups of animals that experience REM sleep.  J. Allan Hobson (2009) has proposed a two level theory of consciousness that would explain the differences between what has historically been called alternate states of consciousness.  The primary level of consciousness, which animals experience, is emotions and perceptions of the outward environment.  But the second level of consciousness, which is applicable mainly to human beings, is language, reflective self-awareness, abstract thinking, volition, and metacognition.  The dream world that is experienced primarily in REM sleep would be described as a primary consciousness, whereas waking experience for human beings would be the secondary level of consciousness.  But in order to understand how the secondary level of consciousness develops, further study of the mechanisms of REM sleep and dreaming must be examined.  Indeed, the two processes might be physiologically linked.

Despite the general notion that REM sleep is equitable to dreaming, dreaming can occur outside of the REM stage of the sleep cycle.  The REM dream relationship is not concretely linked; dreaming occurs without REM mechanisms and rather depends on the cortical activations of dream states (Takeuchi, 2005).  The solution that Takeuchi (2005) proposes to this dilemma is that the REM mechanisms underlying dreaming can take place outside of REM sleep.   This would indeed support dreamlike states while awakened or with the effects of a neuropsychological disorder or hallucinogenic substance.  During REM sleep, the cortex has highly increased activity and a blood flow rate over 200% higher than in the wakened state (Chiş, 2009).  REM sleep is considered to be an activation of many normally inhibitory brain structures, which is one of the reasons why dreams are so disorganized and lacking in an absolute structure.  REM sleep is regulated by the pontine brainstem, which is an evolutionarily ancient structure (Hobson, 2009).  This would infer that REM sleep is not equitable with dreaming and that although dreaming requires the cortical activations that occur during REM sleep, dreaming is a more complex and intricate phenomenon.

Originally, dreams were thought to carry mystical power from an alternate dimension or from supernatural beings.  Dreams were sent for a variety of reasons, not the least of which were predictive of future events in shamanistic cultures.  The ancient Greeks had an entire religious tradition of oracles and prophets that would use dreams and psychosis-like visions to allow them to see into the future.  Indeed, philosophers such as Heraclitus and Aristotle rejected such claims and suggested that the dreams were subjective and created by the mind.  These traditions continued until empirical evidence on dreaming began to arise in the early 19th century.  Sigmund Freud, the inventor of psychotherapy, proposed that REM sleep and dreaming was meaningful, related to mental functioning, and could be interpreted in terms of conscious awareness (Franklin & Zyphur, 2005).  Many of his theories are almost entirely disregarded by the scientific community.  However, an evolutionary analysis of dreams should not disregarded or considered outside the scope of scientific study (Franklin & Zyphur, 2005).  Many of the popular beliefs of dreaming are also false.  Despite the popular notion that dreaming occurs only in REM sleep, it has been known to occur during other sleep stages, and even during woken consciousness (Dang-Vu, et al., 2005)  REM is the most highly correlated with dreamful states and therefore is the basis upon which the foundation for the functioning of dreaming must be based.

Dreaming is a prevailing facet of conscious experience that is associated with specific brain states and occurs spontaneously for several hours each night (Schartz, Dang-Vu, Ponz, et al., 2005).  The problem with studying dreaming is that it is completely subject and unquantifiable.  This makes it extremely difficult for empirical evidence to be obtained.  However, there are well delineated cognitions, emotions, and perceptions of experience while dreaming which suggests that there are specific and common neural patterns of activity occurring while asleep (Shwartz et al., 2005).  REM is characterized by sustained cerebral activations, high cortical energy and blood flow and activations of certain areas of the brain (Dang-Vu, et al., 2005).  The brain areas that seem to activate during REM are the potine tegmentum, thalamic nuclei, and the limbic and paralimbic structures (Dang-Vu, et al., 2005). Takeuchi (2005) described REM as showing activation of the pontine tegmentum, amygdala, paralimbic cortex, and parietal operculum; and deactivation of the prefrontal cortex, motor output, and sensory input, and a shift towards an internal stimulation source.  He also showed that the serotonin pathways modulate activation of the cholinergic neurons over aminergetic neurons in the pons, which causes the aminergetic system to demodulate and the cholinergic modulation in the basal forebrain and ganglia (Takeuchi, 2005).  These are the physiological states corresponding to dreamlike experiences.  These specific brain areas are highly linked to memory, which may be why traces of awakened memory are active while asleep.

The actual role that dreams play in the states of waking consciousness is not fully understood or explainable with current empirical data.  Some of the more contemporary theories are that dreams are a kind of mental rehearsal, hence why many dreams are constituted of the experiencer escaping from imaginary assailants, forgetting certain things only to remember them upon waking, or social situations that could occur in waking life (Franklin, & Zyphur, 2005).  Basically what these theories state is that the dream states have evolved for the purpose of providing the brain with preparation for mental activity during waking consciousness.  Unfortunately, this data is merely speculative, and no real function can be assigned to the dream-state besides the physiological regulation of neural activity and plasticity.  This is not to say that dreams are not useful, only that these hypotheses are not currently empirically testable, leaving them somewhat useless, however compelling they may be.  The brain functions of the activation and deactivation that dynamically oscillate in REM sleep for waking cognition remain unclear (Braun, 2009).

Using Hubson’s (2009) separation of primary and secondary consciousness, the development of human and animal consciousness can be analyzed.  There is a large amount of REM sleep in early life; in humans REM sleep peaks in the third trimester of gestation and decreases significantly after birth, as time awake and cognitive capabilities increase.  Therefore, the primary consciousness declines and the secondary consciousness grows with the development of cortical functioning and the capacity for prolonged periods of wakefulness (Hubson, 2009).  REM sleep occurs at the earliest stages of development; however, it is likely that dreams do not manifest themselves until brain development has reached a point were narratives of subjectivity become possible; in human beings this is around ages five to eight (Hubson, 2009).  Examination of fetal development will provide further insight into the discussion of conscious experience and how REM sleep relates to dreaming.

In the uterus, the human fetus alternates between states of REM and cortical deactivation (Hubson, 2009).  About fifty to eighty percent of the time in the womb is spent in REM sleep (McCarley, 2011).  It is also believed that this autoexcitation that occurs during REM sleep may provide the framework for what is known as waking consciousness (Hubson, 2009).  Evidence has also been provided that the activity of REM sleep facilitates the development of the visual system, especially in specialized development of the striate cortices (Dang-Vu, et al., 2005). 

During REM sleep, temporo-occipital activations were observed using fMRI imaging techniques; these areas included the inferior temporal cortex and fusiform gyrus; however, the functional relationship between the activation of extrastriate cortex caused the deactivation of the striate cortex (Dang-Vu, et al., 2005).  These activities combined the with paralimbic/limbic brain activations create a system where internal information processing occurs in a closed system, not involved in input from the environment or output to the environment.  It is these primary structures in the cortex that can be associated with the disorganized brain functioning exhibited in dreams and that results in highly charged emotion, visual disorganization, and inability of the brain to recognize that it is asleep. These activations combined with deactivations of the association cortices in the inferior and middle lateral prefrontal, the inferior parietal lobule, and the temporo-parietal regions create the effects of dreaming on the brain (Dang-Vu, et al., 2005).  These are the neural correlates known about the phenomenon of dreaming.

The cortical processes activate what is creates the mental states known as dream.  These are highly creative conscious experiences with enormous amounts of cortical activation that differs greatly from waking perception.  During the past decade, the neuroimaging techniques developed has vastly increased the knowledge of the cortical functioning of REM sleep and dreaming; giving science a fundamental knowledge of why the cortex creates input while simultaneously disallowing output of the cortex (Maquet, et al., 2005).  This realm of subjective experience has implications for the consciousness of all mammals and some birds that fit the category of conscious beings, in the first level that Hobson (2005) describes.  The waking consciousness creating the secondary features of Hobson’s protoconsciousness theories are probably exclusive to humans, because of the highly evolved cortical structure that accompanies our brains.

There are ways of altering consciousness to increase the productivity of the REM sleep received.  It seems that yoga is one of the ways, as well as different types of meditation and breathing techniques.  The practitioners of yoga can experience enhance theta-alpha brainwaves and enhanced REM sleep with regular practice (Sulekha, et al., 2006).  This could be an indication that yoga leads to a type of heightened consciousness, because of the types of brain activity involved with REM sleep, and the increases in the brain activity of yogic practitioners.  This is one way that REM sleep may be improved.  Another known way to increase the amount of REM sleep obtained is exercise and mental activity during the day.  REM sleep is essential to conscious functioning and the secondary aspects of consciousness.  Studies done with rats have shown death due to lack of REM sleep, using the disk-over-water method (Cirelli, & Tononi, 2011).  REM sleep is used to regulate cortical functioning and animal studies have shown marked decreases in the functioning of the cortices of REM sleep deprived rats on a cellular level (Cirelli, & Tononi, 2011).  The reasons that Circelli and Tonomi (2011) provide for this is that the protein synthesis and neural plasticity in synaptic consolidation and downscaling are not able to occur; this also suggests that sleep plays a role in the maintenance of the cortical membrane, including glial cells.  REM sleep is an indispensible aspect of consciousness and is perhaps the most important state for the maintenance of the secondary traits of consciousness that human beings experience.


Neuropsychological Disorders

There are several neuropsychological disorders that can provide insight into conscious experience.  The disorders of particular interest to the realm of cognitive construction of perception are those that are influenced by hallucinations, especially visual hallucinations, because of their similarity to dreaming.  These disorders are important for understanding how the perceiver constructs the environment.  They can provide insight into the nature of the construction consciousness and how it manifests itself.  The disorders that will be examined pertaining to this constructive perception are Guillain-Barré syndrome, schizophrenia, narcolepsy, and insomnia.

Guillain-Barré syndrome (GBS) is an acute psychological disorder with sensory and motor impairments (Cochen, et al., 2005).  Many of the patients with this disorder experience mental status disorders, including personality changes, mental disturbances, hallucinatory experiences and oneiric states, dream-like scenic hallucinations, and psychosis.  This syndrome affects the peripheral nervous system; however, the central nervous system is also largely affected, as evidenced by the mental abnormalities (Cochen, et al., 2005). 

The dreams experienced by a small portion of the patients with mental status abnormalities and the dream state would impede upon their waking consciousness.  Many also experienced hallucinations of objects and highly emotional dreams while asleep, perhaps evidencing abnormalities in the amygdala system and its processing and regulation of dreams.  Many patients would experience body illusory body tilts and some even reported sensations of weightless floating (Cochen, et al., 2005).  Many patients saw small hallucinations of goblins, tiny moving figures of various sizes.  These hallucinations generally occurred when the patients closed their eyes, perhaps having to do with the visual cortex’s inability to inhibit activity.  The quality and amounts of sleep were poor in all groups and was fragmented and unstable.  The REM sleep of patients was extremely abnormal and would impede upon the other sleep stages (Cochen, et al., 2005), as it was probably also impeding upon their woken consciousness.  These sufferers of GBS had altered perceptions of the world, probably a result of the severe impairments of the cortical network underlying REM sleep, which resulted in the hallucinations, and lack of the functionality of secondary features of consciousness described by Hobson (2005).

The second disorder that provides information on the consciousness is Narcolepsy.  This disorder is most often conceptualized as affecting regular sleep patterns, especially on REM sleep.  There seems to be a dramatic decrease of the time interval between the onset of sleep and the first cycle of REM sleep, which would support the increase of pressure of the need for REM upon the mind (Dahmen, et al., 2002).  Hallucinations are often experienced before falling asleep and after waking, decreased muscle ton as a result of impairment of the motor system.  Sleep paralysis and sleep attacks can often occur in the disorder.  This disorder is considered a sleep disorder because during the onset of these symptoms, encephalographic data has shown that REM sleep waveforms are present (Dahmen, et al., 2002). 

Schizophrenic hallucinations have also been linked to the intrusion of REM sleep into the waking consciousness.  This REM sleep intrusion into waking life has also been implicated in Parkinson’s disease, including hallucinations, delusions, and REM sleep intrusions (Diederich, et al., 2007).  Schizophrenia and narcolepsy are often hard to differentiate in clinical diagnoses because of the completely altered sleep patterns and the intrusions of REM sleep into waking consciousness (Dahmen, et al., 2002).  This provides evidence that the cortical network associated with REM sleep are malfunctioning, specifically that they are not inhibited as they usually are during waking consciousness.  This also evidences the idea that REM sleep is the foundation upon which the secondary traits of waking consciousness are supported. 

Insomnia is believed to occur because of the increased activation of the limbic and paralimbic regions of the brain (Desseilles, 2008).  Depression is the most common primary diagnosis in patients suffering from insomnia (Desseilles, 2008).  The hyperarousal associated of the cortical mechanisms with both disorders suggest that the sleep dysfunction is due to malfunction of the cortical sleeping system.  The increased density of REM sleep occurrence also provides evidence for this hypothesis.  Insomnia can be highly debilitating to waking consciousness and inhibits many of the cognitive capacities of the secondary traits of consciousness, providing further evidence for Hobson’s theory of consciousness.

These psychological disorders provide some insight into the importance of dreaming as a cortical framework for consciousness.  These deviations upon what would be considered normal human cortical functioning provide evidence of the structural dependency of the brain upon the cortical system underlying REM sleep, and therefore, the subjective experiences of consciousness.


Hallucinogenic Substances

            There are several hallucinogenic substances that can provide further insight into the realm of consciousness.  Lysergic Acid Diethylamide and psilocybin are the two substances that have historically been used to alter waking consciousness.  These two substances have extraordinary impacts upon functioning and alter the state of consciousness to something that is hardly recognizable as either waking or dreaming states of conscious subjective experience.  Instead, these states can be viewed as a kind of limbo in which the cortical mechanisms are altered to create a pseudo-dreamlike state.

            LSD was used largely in the earlier 20th century as an aid to psychotherapy.  The primary changes that occur when under the influence of this substance are illusions, pseudo-hallucinations, synesthesia, alterations of thinking, and inability to correctly perceive time (Passie, et al., 2008).  During this state, motor functions are impaired and attention and concentration are significantly inhibited.  Some scientists have equated the regression of intellectual function under LSD to that of an ontogenetically younger state of consciousness (Passie, et al., 2008).  However, overdoses of LSD can create persisting hallucinations that the DSM recognizes as Hallucinogen Persisting Perceptual Disorder (Iaria, et al., 2010).  This data is supportive of the idea that LSD creates a pseudo consciousness that is a kind of limbo between the consciousness of dreams and the consciousness of waking, combining features to create an altered state of consciousness.  This is consistent with the previous data on the correlates of consciousness as created by a cortical system; indeed, consciousness is a direct result of brain activity of certain complexes.

            Psilocybin can also provide interesting commentary on the nature of conscious perception.  Many of the effects of psilocybin are consistent with those of schizophrenia, especially patients with acute schizophrenia experiencing different types of hallucinations (Mayfrank, et al., 2002).  This hallucinogen has been found to induce hyperfrontal patterns of activation in cerebral blood flow.  Psychomotor retardation was also observed by decreased reaction times in a spatial cueing task (Mayfrank, et al., 2002).  This decrease in cognitive functioning is evidence that psilocybin is also a drug that can induce a pseudo dream state and that the higher processes of attention and the secondary aspects of consciousness are specific to the complex brain organization of human beings.

            These drugs provide evidence that consciousness is but a result of neural functioning and that the specific brain areas of human beings create what humans know as subjective conscious experience.  These states of limbo allow for an analysis of consciousness that includes almost all aspects of waking and dreaming perceptions and provide insight into why consciousness occurs and how it manifests itself.


Consciousness and Cognition

            Evidence for consciousness being a state supported by brain mechanisms and cortical inhibitions and activations that produce what human beings perceive as subjective consciousness.  It can be said that this does not provide for the amount of power that consciousness provides life, nor the potential of the individual within his/her subjective experience.  Ervin Laszlo (2006) attempts to redefine this paradigm by shifting the concept of reality with what is scientifically known and proven about quantum mechanics.  Much of what we consider to be real is actualized, that is, it occurs in time and space.  However, one of the problems with this view is that potential states are also a part of reality.  What quantum physics denotes as virtual, can actually be considered reality, because the inability to predict future events (at the level of the quark) creates potential states that are sustainable.  Potential states do not need to be considered mind like, transcendent, or mysterious.  These are simply physical events at the level of a quantum wave that are not actualized.  This contributes to a fairly stimulating view of consciousness.

            Virtual states are mind like events associated with the potential to become actualized (Laszlo, 2006).  Instead of viewing these are virtual states, if we were to classify these as unrealized physical events, then the consciousness like events become an intrinsic part of the universe.  This creates a dichotomy for two aspects of the same stuff, instead of two different kinds of stuff, which can mediate the mind-body problem experienced by philosophers and psychologists alike.  Overall, this view of consciousness as intrinsic in the universe provides structuralists with the ability to explain consciousness in terms of highly complex physical events that may or may not be actualized.

            The fundamental tenets of consciousness are the perception and emotional reactivity to the environment.  With this definition, science can solve the consciousness problem in terms of secondary and primary characteristics, involving actualized and potential states that makes up the subjective experience that each human being experiences (if he/she is conscious).  This provides insight into the importance of the knowledge and understanding of cortical mechanisms and brain functionality.  Consciousness will continue to evolve alongside life, with human beings at the forefront of the evolutionary race until the human race evolves yet again into the next stage of the collective subjective experience known as life.


Chiş, I. E. (2009). The evolution of brain waves in altered states of consciousness (REM sleep and meditation). Human & Veterinary Medicine, 1, 95-102.

Cirelli, C., & Tononi, G. (2011). Molecular neurobiology of sleep. Handbook Of Clinical Neurology / Edited By P.J. Vinken And G.W. Bruyn, 98191-203.

Cochen, V. V., Arnulf, I. I., Demeret, S. S., Neulat, M. L., Gourlet, V. V., Drouot, X. X., & … Bolgert, F. F. (2005). Vivid dreams, hallucinations, psychosis and REM sleep in Guillain–Barré syndrome. Brain: A Journal of Neurology, 128, 2535-2545.

Dahmen, N. N., Kasten, M. M., Mittag, K. K., & Müller, M. J. (2002). Narcoleptic and schizophrenic hallucinations: Implications for differential diagnosis and pathophysiology. The European Journal of Health Economics, 3(Suppl 2), S94-S98.

Dang-Vu, T. T., Desseilles, M. M., Albouy, G. G., Darsaud, A. A., Gais, S. S., Rauchs, G. G., & … Maquet, P. P. (2005). Dreaming: A neuroimaging view. Schweizer Archiv für Neurologie und Psychiatrie, 156, 415-425.

Desseilles, M., Dang-Vu, T., Schabus, M., Sterpenich, V., Maquet, P., & Schwartz, S. (2008). Neuroimaging insights into the pathophysiology of sleep disorders. Sleep, 31, 777-794.

Diederich, N. J., Leurgans, S., Wenqing, F., Chmura, T. A., & Goetz, C. G. (2008). Visual hallucinations and symptoms of REM sleep behavior disorder in Parkinsonian tauopathies. International Journal of Geriatric Psychiatry, 23, 598-603.

Franklin, M. S., & Zyphur, M. J. (2005). The Role of Dreams in the Evolution of the Human Mind.Evolutionary Psychology, 359-78.

Gouzoulis-Mayfrank, E., Thelen, B., Maier, S., Heekeren, K., Kovar, K., Sass, H., & Spitzer, M. (2002). Effects of the hallucinogen psilocybin on covert orienting of visual attention in humans.Neuropsychobiology, 45, 205-212.

Hobson, J. (2009). REM sleep and dreaming: towards a theory of protoconsciousness. Nature Reviews Neuroscience, 10, 803-813.

Iaria, G., Fox, C., Scheel, M., Stowe, R., & Barton, J. (2010). A case of persistent visual hallucinations of faces following LSD abuse: a functional Magnetic Resonance Imaging study. Neurocase (Psychology Press), 16, 106-118.

Laszlo, E. (2006). Quantum and Consciousness: In Search of a New Paradigm. Zygon: Journal of Religion & Science, 41, 533-542.

Maquet, P., Ruby, P., Maudoux, A., Albouy, G., Sterpenich, V., Dang-Vu, T., & … Laureys, S. (2005). Human cognition during REM sleep and the activity profile within frontal and parietal cortices: a reappraisal of functional neuroimaging data. Progress In Brain Research, 150219-227.

McCarley, R. (2011). Neurobiology of REM sleep. Handbook Of Clinical Neurology / Edited By P.J. Vinken And G.W. Bruyn, 98151-171.

Passie, T., Halpern, J., Stichtenoth, D., Emrich, H., & Hintzen, A. (2008). The pharmacology of lysergic acid diethylamide: a review. CNS Neuroscience & Therapeutics, 14(4), 295-314.

Picchioni, D., Killgore, W. S., Balkin, T. J., & Braun, A. R. (2009). Positron Emission Tomography Correlates of Visually-Scored Electroencephalographic Waveforms During Non-Rapid Eye Movement Sleep.International Journal of Neuroscience, 119, 2074-2099.

Schwartz, S. S., Dang-Vu, T. T., Ponz, A. A., Duhoux, S. S., & Maquet, P. P. (2005). Dreaming: A neuropsychological view. Schweizer Archiv für Neurologie und Psychiatrie, 156, 426-439.

Takeuchi, T. (2005). Dream mechanisms: Is REM sleep indispensable for dreaming?. Sleep & Biological Rhythms, 3, 56-63.