Tsuchiya, N. & Koch, C. (August 2005). Continuous flash suppression reduces negative afterimages. Nature Neuroscience, Vol. 8, No. 8, 1096-1101.
Continuous flash suppression (CFS) is a tool that can be used to reliably suppress vivid images from conscious awareness for long periods of time. Here, different patterned images ("Mondrians") are flashed rapidly into one eye while input to the corresponding location in the other eye remains fixed, the latter typically remaining unseen often for durations greater than ten times what can be achieved with binocular rivalry or other masking methods, even though the image remains present on the retina for several minutes. Interestingly, researchers discovered that negative afterimages or "photogenes", effects lingering in view after termination of the visual stimulus, also seem to be diminished with exposure to CFS. Though it is widely believed that afterimages originate among retinal neurons, this evidence supports the conclusion that the weakened afterimage must be due to interference from sites at or beyond binocular convergence, such as the lateral geniculate nucleus (LGN) or cortex. Specifically, it must be an area which receives input from both eyes but does not correspond directly to the neuronal correlates of perceptual awareness. The results hint at differences between concepts of attention and awareness.
Showing posts with label Vision. Show all posts
Showing posts with label Vision. Show all posts
Wednesday, May 7, 2008
Friday, April 25, 2008
Neuronal activity related to faces and matching
Ojemann, J.G., Ojemann, G.A., & Lettich, E. (1992). Neuronal activity related to faces and matching in human right nondominant temporal cortex. Brain, 115, 1-13.
Using microelectrode recording, this group set out to look at changes in neuronal activity in response to faces, previously described in monkey cortex but not well established in humans. Recording was restricted to areas of right anterior temporal cortex that would be later resected in an epileptic lobectomy, areas that showed the least epileptic activity on electrocorticography. Seven neuronal populations related to face perception were identified. In addition, three other populations, only in middle temporal gyrus, increased activity with the labelling of the emotional expression of a face. The ease with which a given task can elicit specific, temporally-coupled changes in neuronal activity suggest that human association cortex is compartmentalized into behaviorally specific systems.
Using microelectrode recording, this group set out to look at changes in neuronal activity in response to faces, previously described in monkey cortex but not well established in humans. Recording was restricted to areas of right anterior temporal cortex that would be later resected in an epileptic lobectomy, areas that showed the least epileptic activity on electrocorticography. Seven neuronal populations related to face perception were identified. In addition, three other populations, only in middle temporal gyrus, increased activity with the labelling of the emotional expression of a face. The ease with which a given task can elicit specific, temporally-coupled changes in neuronal activity suggest that human association cortex is compartmentalized into behaviorally specific systems.
Thursday, April 17, 2008
The Visual Cliff
Gibson, E.J. & Walk, R.D. (April 1960). The "Visual Cliff". Scientific American.
To investigate depth perception in human and animal species, these authors created the "visual cliff" which allowed them to experimentally adjust the optical and tactical stimuli associated with a simulated cliff while protecting the subjects from injury. They discovered that all species can perceive and avoid a sharp drop by the time they take up independent locomotion, be it at Day 1 in chicks, 4 weeks in rats, or 6 months in humans. Most rely on visual cues for depth perception. The rat, however, relies predominantly on tactual cues (being nocturnal) but will fall back on sound vision when needed. Next, the experimenters wanted to find out which visual cues played the decisive role in depth perception. Using dark-reared animals, they concluded motion parallax is an innate cue for depth discrimination, whereas responses to differential pattern-density may be learned later.
(I, Doug G, am the author of this article, The Visual Cliff, and I release its content under the terms of the GNU Free Documentation License, Version 1.2 and later.)
To investigate depth perception in human and animal species, these authors created the "visual cliff" which allowed them to experimentally adjust the optical and tactical stimuli associated with a simulated cliff while protecting the subjects from injury. They discovered that all species can perceive and avoid a sharp drop by the time they take up independent locomotion, be it at Day 1 in chicks, 4 weeks in rats, or 6 months in humans. Most rely on visual cues for depth perception. The rat, however, relies predominantly on tactual cues (being nocturnal) but will fall back on sound vision when needed. Next, the experimenters wanted to find out which visual cues played the decisive role in depth perception. Using dark-reared animals, they concluded motion parallax is an innate cue for depth discrimination, whereas responses to differential pattern-density may be learned later.
(I, Doug G, am the author of this article, The Visual Cliff, and I release its content under the terms of the GNU Free Documentation License, Version 1.2 and later.)
Wednesday, February 20, 2008
Neural fate of ignored stimuli
Yi, D. et al. (September 2004). Neural fate of ignored stimuli: dissociable effects of perceptual and working memory load. Nature Neuroscience, Volume 7, Number 9, 992-996.
After some debate over whether attention acts a filter early in the processing hierarchy ("early selection") or whether it blocks awareness of perceptually encoded stimuli at a late stage of processing ("late selection"), the field has accepted both accounts to some degree. When task difficulty is low, late selection may be more likely, whereas aggressive early selection may be more common when task difficulty is high. However, task difficulty can be defined in several ways and this paper predicted and confirmed that increasing perceptual demands properly constitutes task difficulty and leads to this early selection behavior, whereas increasing working memory loads does not.
Experimentally, subjects were shown faces foveally, surrounded by background images depicting scenes. They were told to fixate on the faces and ignore the background images. Faces were cycled, but so were the background images. In the EASY block, subjects were asked to play a "one-back" game, discriminating between the current face image and face presented prior. Subject performance was high. However, in addition to this primary task, the parahippocampal place area (PPA) showed activity that indicated it was indeed processing the background image changes successfully as well. But as the perceptual load was adjusted, with the HARD block requiring more difficult facial discriminations, it was clear that the PPA was not processing the background scenes to the same extent as in the low perceptual load condition. By comparison, the MEMORY block, in which "two-back" rules required subjects to maintain more information in working memory for longer, did not demonstrate these attenuation effects on background processing, i.e. the PPA was still successfully detecting background changes. This indicated, as hypothesized, that perceptual demands and working memory load result in differential attentional effects.
After some debate over whether attention acts a filter early in the processing hierarchy ("early selection") or whether it blocks awareness of perceptually encoded stimuli at a late stage of processing ("late selection"), the field has accepted both accounts to some degree. When task difficulty is low, late selection may be more likely, whereas aggressive early selection may be more common when task difficulty is high. However, task difficulty can be defined in several ways and this paper predicted and confirmed that increasing perceptual demands properly constitutes task difficulty and leads to this early selection behavior, whereas increasing working memory loads does not.
Experimentally, subjects were shown faces foveally, surrounded by background images depicting scenes. They were told to fixate on the faces and ignore the background images. Faces were cycled, but so were the background images. In the EASY block, subjects were asked to play a "one-back" game, discriminating between the current face image and face presented prior. Subject performance was high. However, in addition to this primary task, the parahippocampal place area (PPA) showed activity that indicated it was indeed processing the background image changes successfully as well. But as the perceptual load was adjusted, with the HARD block requiring more difficult facial discriminations, it was clear that the PPA was not processing the background scenes to the same extent as in the low perceptual load condition. By comparison, the MEMORY block, in which "two-back" rules required subjects to maintain more information in working memory for longer, did not demonstrate these attenuation effects on background processing, i.e. the PPA was still successfully detecting background changes. This indicated, as hypothesized, that perceptual demands and working memory load result in differential attentional effects.
Sunday, February 17, 2008
Control of goal-directed and stimulus-driven attention
Corbetta, M. & Shulam, G.L. (March 2002). Control of goal-directed and stimulus-driven attention in the brain. Nature Reviews Neuroscience, Volume 3, 201 - 215.
This paper proposes that visual attention (orienting) is controlled by two interacting networks. One system which is centered on the dorsal posterior parietal and frontal cortex, is involved in the cognitive, top-down, goal-directed selection of sensory information and responses. The second system, largely lateralized to the right hemisphere, is centered on the temporoparietal and ventral frontal cortex and is specialized for the detection of behaviorally-relevant stimuli, particularly when they are salient or unexpected. The second network reflects stimulus-driven, bottom-up control of attention, and can be seen as a 'circuit-breaker' of the first network, interrupting ongoing cognitive activity and directing attention to stimuli outside the focus of current processing when necessary.
This paper proposes that visual attention (orienting) is controlled by two interacting networks. One system which is centered on the dorsal posterior parietal and frontal cortex, is involved in the cognitive, top-down, goal-directed selection of sensory information and responses. The second system, largely lateralized to the right hemisphere, is centered on the temporoparietal and ventral frontal cortex and is specialized for the detection of behaviorally-relevant stimuli, particularly when they are salient or unexpected. The second network reflects stimulus-driven, bottom-up control of attention, and can be seen as a 'circuit-breaker' of the first network, interrupting ongoing cognitive activity and directing attention to stimuli outside the focus of current processing when necessary.
Saturday, February 16, 2008
Visual Attention
Kanwisher, N. & Wojciulik, E. (November 2000). Visual Attention: Insights from Brain Imaging. Nature Reviews: Neuroscience, Volume 1, 91-98.
This review discusses four major questions related to attention's role in visual processing. First, where in the visual pathway does attention act? Second, what is able to be selected by attention? Third, how does attention affect neural responses? And fourth, where do attentional signals comes from?
Where in the visual pathway does attention act? It has been known for some time that substantial effects of attention can be found in the extrastriate cortex. However, it was not until recently that attentional modulation was discovered in earlier stages of the visual processing pathway (e.g. primary visual cortex). This may be more common when the processing load is considered high.
What gets selected by attention? Under different conditions, attention can select spatial locations, feature dimensions, whole visual objects, or even a combination thereof. However, these may not always be deployed with perfect control.
How does attention affect neural responses? Evidence exists which supports attention influence as being characterized as multiplicative (gain modulations) and/or additive (baseline shifts). And some postulate that increasing baseline activity in a neural population may bring these cells into a dynamic range where the same stimulus input will produce larger responses.
What is the source of attentional signals? Researchers have implicated the fronto-parietal network in providing top-down biasing signals to visual regions, and speculate that this system supports a very heterogeneous set of attention tasks.
This review discusses four major questions related to attention's role in visual processing. First, where in the visual pathway does attention act? Second, what is able to be selected by attention? Third, how does attention affect neural responses? And fourth, where do attentional signals comes from?
Where in the visual pathway does attention act? It has been known for some time that substantial effects of attention can be found in the extrastriate cortex. However, it was not until recently that attentional modulation was discovered in earlier stages of the visual processing pathway (e.g. primary visual cortex). This may be more common when the processing load is considered high.
What gets selected by attention? Under different conditions, attention can select spatial locations, feature dimensions, whole visual objects, or even a combination thereof. However, these may not always be deployed with perfect control.
How does attention affect neural responses? Evidence exists which supports attention influence as being characterized as multiplicative (gain modulations) and/or additive (baseline shifts). And some postulate that increasing baseline activity in a neural population may bring these cells into a dynamic range where the same stimulus input will produce larger responses.
What is the source of attentional signals? Researchers have implicated the fronto-parietal network in providing top-down biasing signals to visual regions, and speculate that this system supports a very heterogeneous set of attention tasks.
Friday, February 15, 2008
Subcortical Face Processing
Johnson, M.H. (October 2005). Subcortical Face Processing. Nature Neuroscience Reviews, Volume 6, 766-774.
The most well-known visual pathway uses parvocellular channels from the retina to the LGN and on to the primary visual cortex, where very complicated fine-grained image processing is carried out. However, evidence supports multiple visual pathways, and last I checked, 12 different visual pathways have been identified in the brain so far. This review paper discusses a specific subcortical face-detection system which involves the superior colliculus, pulvinar, and amygdala.
Researchers hypothesize that this pathway is more rapid than cortical routes, relies on rather low-fidelity (low-spatial-frequency) visual information, and can critically modulate cortical processing. One characterization is that this pathway is important for directing emotional attention, providing an emotional flavoring to higher-order visual processing. As this pathway is thought to bias the cortical processing of visual input -- detecting the prescence of faces, orienting us towards them, and activating dependent cortical regions -- this may a particularly important pathway during development when cortical structures (such as the fusiform face area, orbitofrontal cortices, and other cortical regions involved in the social brain network) are still being molded. Atypical processing of socially salient stimuli, seen in such disorders as autism, Turner syndrome, and Williams syndrome, may be associated with a failures in this subcortical pathways, leading to improper development and specialization of dependent cortical circuits.
The most well-known visual pathway uses parvocellular channels from the retina to the LGN and on to the primary visual cortex, where very complicated fine-grained image processing is carried out. However, evidence supports multiple visual pathways, and last I checked, 12 different visual pathways have been identified in the brain so far. This review paper discusses a specific subcortical face-detection system which involves the superior colliculus, pulvinar, and amygdala.
Researchers hypothesize that this pathway is more rapid than cortical routes, relies on rather low-fidelity (low-spatial-frequency) visual information, and can critically modulate cortical processing. One characterization is that this pathway is important for directing emotional attention, providing an emotional flavoring to higher-order visual processing. As this pathway is thought to bias the cortical processing of visual input -- detecting the prescence of faces, orienting us towards them, and activating dependent cortical regions -- this may a particularly important pathway during development when cortical structures (such as the fusiform face area, orbitofrontal cortices, and other cortical regions involved in the social brain network) are still being molded. Atypical processing of socially salient stimuli, seen in such disorders as autism, Turner syndrome, and Williams syndrome, may be associated with a failures in this subcortical pathways, leading to improper development and specialization of dependent cortical circuits.
Wednesday, February 13, 2008
Differential processing of objects under various viewing conditions in the human LOC
Grill-Spector, K. et al. (September 1999). Differential processing of objects under various viewing conditions in the human lateral occipital complex. Neuron, Vol. 24, 187-203.
This study used fMRIa techniques to investigate the brain's object-selective regions (namely the lateral occipital complex). fMRIa assumes that a group of neurons will respond to repeated presentations of a stimulus with attenuated responses. This signal reduction is presumably the result of neural fatigue from repeated exposure. Thus, "adaptation" data can be used to identify which types of stimulus are effectively treated identically by a certain region of the brain. This is especially interesting in structures further up the processing hierarchy where lower-level transformations have likely given way to more abstract, general representations of the stimuli. Researchers can then explore what properties of objects are preserved and which are transformed to a canonical representation by the time signals converge on a specific region.
First, the study sought to understand how long adaptation effects last. Time durations as long as 8 sec between matched stimuli still elicited amplitude reductions, establishing that adaptation has a fairly long-lasting effect.
Secondly, the study set out to examine which object properties were invariant within the LOC. The results indicate that the LOC is less sensitive to changes in size and position, compared to changes induced by illumination and viewpoint (rotation). In other words, it seems the LOC receives visual input which has been normalized for size and position.
This study used fMRIa techniques to investigate the brain's object-selective regions (namely the lateral occipital complex). fMRIa assumes that a group of neurons will respond to repeated presentations of a stimulus with attenuated responses. This signal reduction is presumably the result of neural fatigue from repeated exposure. Thus, "adaptation" data can be used to identify which types of stimulus are effectively treated identically by a certain region of the brain. This is especially interesting in structures further up the processing hierarchy where lower-level transformations have likely given way to more abstract, general representations of the stimuli. Researchers can then explore what properties of objects are preserved and which are transformed to a canonical representation by the time signals converge on a specific region.
First, the study sought to understand how long adaptation effects last. Time durations as long as 8 sec between matched stimuli still elicited amplitude reductions, establishing that adaptation has a fairly long-lasting effect.
Secondly, the study set out to examine which object properties were invariant within the LOC. The results indicate that the LOC is less sensitive to changes in size and position, compared to changes induced by illumination and viewpoint (rotation). In other words, it seems the LOC receives visual input which has been normalized for size and position.
fMRIa
Krekelberg, B, Boynton, G.M., & van Wezel, R.J.A. (2006). Adaptation: from single cells to BOLD signals. Trends in Neuroscience.
Functional magnetic resonance imaging adaptation (fMRIa) is an increasingly popular method which takes advantage of the brain changes which occur in response to long exposure to some evocative stimulus. If Stimulus 1 (S1) excites a certain neuronal population, repeated exposure to S1 will result in subsequently attenuated responses. This may be due to neural fatigue (i.e. the more a neuron fires, the more its subsequent responses will be reduced) or may be due to coupled hemodynamic processes. However, when S1 is followed by a unique stimulus, S2, the response amplitudes should not be attenuated as a fresh sub-population of neurons is excited. Using this technique can allow researchers to determine if the same or unique neuronal groups are involved in processing two stimuli. This paper goes on to describe the utility of the technique in examination of the visual system, particularly orientation, motion, and face detection. It also stresses the importance of adaptation timescale in experimental design.
Functional magnetic resonance imaging adaptation (fMRIa) is an increasingly popular method which takes advantage of the brain changes which occur in response to long exposure to some evocative stimulus. If Stimulus 1 (S1) excites a certain neuronal population, repeated exposure to S1 will result in subsequently attenuated responses. This may be due to neural fatigue (i.e. the more a neuron fires, the more its subsequent responses will be reduced) or may be due to coupled hemodynamic processes. However, when S1 is followed by a unique stimulus, S2, the response amplitudes should not be attenuated as a fresh sub-population of neurons is excited. Using this technique can allow researchers to determine if the same or unique neuronal groups are involved in processing two stimuli. This paper goes on to describe the utility of the technique in examination of the visual system, particularly orientation, motion, and face detection. It also stresses the importance of adaptation timescale in experimental design.
Sunday, February 10, 2008
Retinotopy and Functional Subdivision of Human Areas MT and MST
Huk, A.C. et al. (August 15, 2002). Retinotopy and Functional Subdivision of Human Areas MT and MST. The Journal of Neuroscience, Volume 22, Number 16, 7195-7205.
Much research in neuroscience has begun with animal studies (and invasive techniques) and only later been continued with human subjects (with predominantly non-invasive methodologies). This paper discusses the attempts to reconcile the areas of visual cortex responsible for detecting visual motion in the macaque and the human. In particular, two sub-divisions of the dorsal superior temporal sulcus (STS) are well-studied in the macaque: the middle temporal (MT) and the medial superior temporal (MST) visual areas. The MT is characterized by a distinguishable retinotopic map and a coarse-grained small receptive field, whereas the MST is just the opposite. This experiment was designed to recognize areas displaying these characteristics in the human MT+ or V5 area, thought to be homologous to the macaque STS, using fMRI. Subregions of the human MT+ were tentatively identified, bridging the gap between animal and human research.
Much research in neuroscience has begun with animal studies (and invasive techniques) and only later been continued with human subjects (with predominantly non-invasive methodologies). This paper discusses the attempts to reconcile the areas of visual cortex responsible for detecting visual motion in the macaque and the human. In particular, two sub-divisions of the dorsal superior temporal sulcus (STS) are well-studied in the macaque: the middle temporal (MT) and the medial superior temporal (MST) visual areas. The MT is characterized by a distinguishable retinotopic map and a coarse-grained small receptive field, whereas the MST is just the opposite. This experiment was designed to recognize areas displaying these characteristics in the human MT+ or V5 area, thought to be homologous to the macaque STS, using fMRI. Subregions of the human MT+ were tentatively identified, bridging the gap between animal and human research.
New images from human visual cortex
R.B.h. Tootell et al. (1996). New images from human visual cortex. Trends in Neuroscience, Vol. 19, No. 11, 481-489.
This article takes aim at broadly reviewing animal and human studies of the human visual cortex. There has been a long and successful tradition of studying the visual cortex in our Old World monkey relatives, the macaques. Although there are significant differences, there are also striking similarities and key learnings that can be generalized from examination of macaque cortex. The article discusses the attempts to converge the research in these two different disciplines of human and animal studies on the basis of functional properties, retinotopy, histology, and connectivity. Among others, it covers the principles of disproportionate cortical mapping, cortical flattening (or unfolding) techniques common to animal studies, and the 'where' vs. 'what' pathways of the visual system. Although these two distinct pathways are well understood in the monkey, they are defined with more uncertainty in the human. The article discusses motion processing and spatial organization in the dorsal 'where' pathway, and color processing, form recognition, and object identification in the ventral 'what' pathway.
This article takes aim at broadly reviewing animal and human studies of the human visual cortex. There has been a long and successful tradition of studying the visual cortex in our Old World monkey relatives, the macaques. Although there are significant differences, there are also striking similarities and key learnings that can be generalized from examination of macaque cortex. The article discusses the attempts to converge the research in these two different disciplines of human and animal studies on the basis of functional properties, retinotopy, histology, and connectivity. Among others, it covers the principles of disproportionate cortical mapping, cortical flattening (or unfolding) techniques common to animal studies, and the 'where' vs. 'what' pathways of the visual system. Although these two distinct pathways are well understood in the monkey, they are defined with more uncertainty in the human. The article discusses motion processing and spatial organization in the dorsal 'where' pathway, and color processing, form recognition, and object identification in the ventral 'what' pathway.
Wednesday, February 6, 2008
A flexible fusiform area for subordinate-level visual processing automatized by expertise
Tarr, M.J. & Gauthier, I. (August 2000). FFA: A flexible fusiform area for subordinate-level visual processing automatized by expertise. Nature Neuroscience, Volume 3, Number 8, 764-769.
The article explores the controversy over face perception in the fusiform gyrus. Is face perception carried out by domain-specific mechanisms specialized for processing faces in particular, or are faces handled by domain-general mechanisms? This article argues for the latter alternative. Specifically, it emphasizes categorization and expertise in a given object domain (e.g. faces, cars) affect the response of the fusiform area independent of stimulus geometry. Counter-evidence and rebuttals are too complicated to get into in such a summary. However, the heatedness of the debate leaves this issue far from closed.
The article explores the controversy over face perception in the fusiform gyrus. Is face perception carried out by domain-specific mechanisms specialized for processing faces in particular, or are faces handled by domain-general mechanisms? This article argues for the latter alternative. Specifically, it emphasizes categorization and expertise in a given object domain (e.g. faces, cars) affect the response of the fusiform area independent of stimulus geometry. Counter-evidence and rebuttals are too complicated to get into in such a summary. However, the heatedness of the debate leaves this issue far from closed.
Domain specificity in face perception
Kanwisher, N. (August 2000). Domain specificity in face perception. Nature Neuroscience, Volume 3, Number 8, 759-763.
The article explores the controversy over face perception in the fusiform gyrus. Is face perception carried out by domain-specific mechanisms specialized for processing faces in particular, or are faces handled by domain-general mechanisms? This article argues for the former alternative. It uses inversion, holistic recognition advantages, and a double-dissociation between face and object recognition found in the neuropsychological record (prosopagnosia patients who cannot recognize faces but who can recognize objects and C.K. who is impaired in reading and object recognition but whose facial recognition is preserved) as primary pieces of evidence. Counter-evidence and rebuttals are too complicated to get into in such a summary. However, the case seems far from closed.
The article explores the controversy over face perception in the fusiform gyrus. Is face perception carried out by domain-specific mechanisms specialized for processing faces in particular, or are faces handled by domain-general mechanisms? This article argues for the former alternative. It uses inversion, holistic recognition advantages, and a double-dissociation between face and object recognition found in the neuropsychological record (prosopagnosia patients who cannot recognize faces but who can recognize objects and C.K. who is impaired in reading and object recognition but whose facial recognition is preserved) as primary pieces of evidence. Counter-evidence and rebuttals are too complicated to get into in such a summary. However, the case seems far from closed.
Saturday, December 1, 2007
Vision: A Window on Consciousness
Logothetis, N.K. (November 1999). Vision: A Window on Consciousness, Scientific American.
In this article, Nikos k. Logothetis, Director of the physiology of cognitive processes division at the Max Planck Institute in Germany, summarizes some recent research attempting to grope at the problem of consciousness.
What is consciousness? What are we actually conscious of? Is there a consciousness cortex? Or shy of that, are there certain pockets of neurons well correlated with subjective awareness? Neuroscience has grown increasingly concerned with these questions as it has grown increasingly more equipped to answer them. Logothetis scopes the article to a discussion of experiments related to visual awareness. As our visual processing is far and away the most adept sensory system, it is an important place to begin study.
Inspired by ambiguous stimuli (such as Necker Cubes and Salvador Dali paintings), which can be useful in experiments designed to reach consciousness, Logothetis describes how experiments involving binocular rivalry have show promising initial results. In binocular rivalry, the visual system is exposed to two “opposing” images, one in each eye, which can be difficult to resolve. To the conscious observer, these opposing images appear to alternate in consciousness, the mind becoming aware of one and then the other as the visual system selects one visual stimulus from one eye and then the other. This presents some interesting opportunities for examining the role of consciousness.
Using brain imaging and single cell recording techniques, the researchers reveal that neurons whose behavior reflects perception are distributed throughout the visual pathway. However, earlier stages of the visual pathway do not show behavior related directly to perception as often as later stages of the pathway which more reliably correlate with awareness. As an example, the inferior temporal cortex (ITC), long believed to be important for perceiving form and recognizing objects, appears to be a particularly active region when subjects report seeing faces.Technology has brought us to a place where tools exist in our toolbox for elucidating the mysteries of the mind. However, the sheer complexity of the human brain will ensure that isolating brain structures, pathways, and processes responsible for mediating consciousness will still be a daunting task for future researchers.
In this article, Nikos k. Logothetis, Director of the physiology of cognitive processes division at the Max Planck Institute in Germany, summarizes some recent research attempting to grope at the problem of consciousness.
What is consciousness? What are we actually conscious of? Is there a consciousness cortex? Or shy of that, are there certain pockets of neurons well correlated with subjective awareness? Neuroscience has grown increasingly concerned with these questions as it has grown increasingly more equipped to answer them. Logothetis scopes the article to a discussion of experiments related to visual awareness. As our visual processing is far and away the most adept sensory system, it is an important place to begin study.
Inspired by ambiguous stimuli (such as Necker Cubes and Salvador Dali paintings), which can be useful in experiments designed to reach consciousness, Logothetis describes how experiments involving binocular rivalry have show promising initial results. In binocular rivalry, the visual system is exposed to two “opposing” images, one in each eye, which can be difficult to resolve. To the conscious observer, these opposing images appear to alternate in consciousness, the mind becoming aware of one and then the other as the visual system selects one visual stimulus from one eye and then the other. This presents some interesting opportunities for examining the role of consciousness.
Using brain imaging and single cell recording techniques, the researchers reveal that neurons whose behavior reflects perception are distributed throughout the visual pathway. However, earlier stages of the visual pathway do not show behavior related directly to perception as often as later stages of the pathway which more reliably correlate with awareness. As an example, the inferior temporal cortex (ITC), long believed to be important for perceiving form and recognizing objects, appears to be a particularly active region when subjects report seeing faces.Technology has brought us to a place where tools exist in our toolbox for elucidating the mysteries of the mind. However, the sheer complexity of the human brain will ensure that isolating brain structures, pathways, and processes responsible for mediating consciousness will still be a daunting task for future researchers.
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