Visual modularity
Encyclopedia
In cognitive neuroscience
, visual modularity is an organizational concept concerning how vision
works. The way in which the primate
visual system
operates is currently under intense scientific scrutiny. One dominant thesis is that different properties of the visual world (color
, motion
, form
and so forth) require different computational solutions which are implemented in anatomically/functionally distinct regions that operate independently – that is, in a modular fashion.
is an intriguing condition brought about by damage to the Extrastriate cortex
MT+ that renders humans and monkeys unable to perceive motion, seeing the world in a series of static "frames" instead and indicates that there might be a "motion centre" in the brain. Of course, such data can only indicate that this area is at least necessary to motion perception, not that it is sufficient; however, other evidence has shown the importance of this area to primate motion perception. Specifically, physiological, neuroimaging, perceptual, electrical- and transcranial magnetic stimulation
evidence (Table 1) all come together on the area V5/hMT+. Converging evidence of this type is supportive of a module for motion processing. However, this view is likely to be incomplete: other areas are involved with motion perception
, including V1, V2 and V3a and areas surrounding V5/hMT+ (Table 2). A recent fMRI study put the number of motion areas at twenty-one (Stiers et al., 2006:83). Clearly a stream of diverse anatomical areas. The extent to which this is ‘pure’ is in question: with Akinetopsia come severe difficulties in obtaining structure from motion (Rizzo, Nawrot, Zihl, 1995). V5/hMT+ has since been implicated in this function (Grunewald, Bradley & Andersen, 2002) as well as determining depth (DeAngelis, Cumming and Newsome, 1998). Thus the current evidence suggests that motion processing occurs in a modular stream, although with a role in form and depth perception at higher levels.
) the notion of a "color centre" in the primate brain has had growing support (e.g. Meadows, 1974; Sacks and Wasserman, 1987; Zeki, 1990; Grüsser and Landis, 1991). Again, such clinical evidence only implicates that this region is critical to color perception
and nothing more. Other evidence, however, including neuroimaging
and physiology (Wachtler et al. 2003; Kusunoki, Moutoussis & Zeki, 2006) converges on V4 as necessary to color perception. A recent meta-analysis
has also shown a specific lesion
common to achromats corresponding to V4 (Bouvier and Engel, 2006). From another direction altogether it has been found that when synaesthetes
experience color by a non-visual stimulus V4 is active (Rich et al., 2006; Sperling et al., 2006). On the basis of this evidence it would seem that color processing is modular. However, as with motion processing it is likely that this conclusion is inaccurate. Other evidence shown in Table 3 implicates different areas’ involvement with color. It may thus be more instructive to consider a multistage color processing stream from the retina through to cortical areas including at least V1, V2, V4, PITd and TEO. Consonant with motion perception there appear to be a constellation of areas drawn upon for color perception. In addition, V4 may have a special but not exclusive role. For example, single cell recording has shown only V4 cells respond to the color of a stimuli rather than its waveband, whereas other areas involved with color do not (Wachtler et al. 2003; Kusunoki, Moutoussis & Zeki, 2006).
. The well studied patient DF is unable to recognize or discriminate objects (Mishkin, Ungerleider and Macko, 1983) owing to damage in areas of the lateral occipital cortex (James et al., 2003) although she can see scenes without problem – she can literally see the forest but not the trees (Steeves et al. 2006). Neuroimaging
of intact individuals reveals strong occipito-temporal activation during object presentation and greater activation still for object recognition (see Grill-Spector, 2003). Of course, such activation could be due to other processes, such as visual attention. However, other evidence that shows a tight coupling of perceptual and physiological changes (Sheinberg and Logothetis, 2001) suggests activation in this area does underpin object recognition. Within these regions are more specialized areas for face or fine grained analysis (Gauthier, Skudlarski, Gore and Anderson, 2000), place perception (Epstein & Kanwisher, 1998) and human body perception (Downing, Jiang, Shuman and Kanwisher, 2001). Perhaps some of the strongest evidence for the modular nature of these processing systems is the double dissociation between object- and face (prosop-) agnosia (e.g. Moscowitch, Winocur and Behrmann, 1997). However, as with color and motion, early areas (see Pasupathy, 2006 for a comprehensive review) are implicated too lending support to the idea of a multistage stream terminating in the inferotemporal cortex rather than an isolated module.
" by philosopher Jerry Fodor
(1983). A detailed application of this idea to the case of vision was published by Pylyshyn (1999), who argued that there is a significant part of vision that is not responsive to beliefs and is "cognitively impenetrable."
Much of the confusion concerning modularity exists in neuroscience because there is evidence for specific areas (e.g. V4 or V5/hMT+) and the concomitant behavioral deficits following brain insult (thus taken as evidence for modularity). In addition, evidence shows other areas are involved and that these areas subserve processing of multiple properties (e.g. V1: see Leventhal et al., 1995) (thus taken as evidence against modularity). That these streams have the same implementation in early visual areas, like V1 is not inconsistent with a modular viewpoint: to adopt the canonical analogy in cognition, it is possible for different software to run on the same hardware. A consideration of psychophysics
and neuropsychological data would suggest support for this. For example, psychophysics has shown that percepts for different properties are realized asynchronously (Moutoussis & Zeki 1997, Viviani & Aymoz, 2001). In addition, although achromats experience other cognitive defects (Gegenfurtner, 2003) they do not have motion or form deficits when their lesion is restricted to V4 (Zeki, 2005). Relatedly, Zihl and colleagues’ (1983) Akinetopsia
patient shows no deficit to color or object perception (although deriving depth and structure from motion is problematic, see above) and object agnostics do not have damaged motion or color perception, making the three disorders triply dissociable. Taken together this evidence suggests that even though distinct properties may employ the same early visual areas they are functionally independent. Furthermore, that the intensity of subjective perceptual experience (e.g. color) correlates with activity in these specific areas (e.g. V4) (Bartels and Zeki, 2005), the recent evidence that synaesthetes
show V4 activation during the perceptual experience of color, as well as the fact that damage to these areas results in concomitant behavioral deficits (the processing may be occurring but perceivers do not have access to the information) are all evidence for visual modularity.
Cognitive neuroscience
Cognitive neuroscience is an academic field concerned with the scientific study of biological substrates underlying cognition, with a specific focus on the neural substrates of mental processes. It addresses the questions of how psychological/cognitive functions are produced by the brain...
, visual modularity is an organizational concept concerning how vision
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
works. The way in which the primate
Primate
A primate is a mammal of the order Primates , which contains prosimians and simians. Primates arose from ancestors that lived in the trees of tropical forests; many primate characteristics represent adaptations to life in this challenging three-dimensional environment...
visual system
Visual system
The visual system is the part of the central nervous system which enables organisms to process visual detail, as well as enabling several non-image forming photoresponse functions. It interprets information from visible light to build a representation of the surrounding world...
operates is currently under intense scientific scrutiny. One dominant thesis is that different properties of the visual world (color
Color
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
, motion
Motion (physics)
In physics, motion is a change in position of an object with respect to time. Change in action is the result of an unbalanced force. Motion is typically described in terms of velocity, acceleration, displacement and time . An object's velocity cannot change unless it is acted upon by a force, as...
, form
Shape
The shape of an object located in some space is a geometrical description of the part of that space occupied by the object, as determined by its external boundary – abstracting from location and orientation in space, size, and other properties such as colour, content, and material...
and so forth) require different computational solutions which are implemented in anatomically/functionally distinct regions that operate independently – that is, in a modular fashion.
Motion processing
AkinetopsiaAkinetopsia
Akinetopsia, also known as cerebral akinetopsia or motion blindness, is an extremely rare neuropsychological disorder in which a patient cannot perceive motion in their visual field, despite being able to see stationary objects without issue. For patients with akinetopsia, the world becomes devoid...
is an intriguing condition brought about by damage to the Extrastriate cortex
Extrastriate cortex
The extrastriate cortex is the region of the occipital cortex of the mammalian brain located next to the primary visual cortex, which is also named striate cortex because of its appeareance in the microscope. The extrastriate cortex encompasses multiple functional areas, including V3, V4, V5/MT...
MT+ that renders humans and monkeys unable to perceive motion, seeing the world in a series of static "frames" instead and indicates that there might be a "motion centre" in the brain. Of course, such data can only indicate that this area is at least necessary to motion perception, not that it is sufficient; however, other evidence has shown the importance of this area to primate motion perception. Specifically, physiological, neuroimaging, perceptual, electrical- and transcranial magnetic stimulation
Transcranial magnetic stimulation
Transcranial magnetic stimulation is a noninvasive method to cause depolarization or hyperpolarization in the neurons of the brain...
evidence (Table 1) all come together on the area V5/hMT+. Converging evidence of this type is supportive of a module for motion processing. However, this view is likely to be incomplete: other areas are involved with motion perception
Motion perception
Motion perception is the process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs...
, including V1, V2 and V3a and areas surrounding V5/hMT+ (Table 2). A recent fMRI study put the number of motion areas at twenty-one (Stiers et al., 2006:83). Clearly a stream of diverse anatomical areas. The extent to which this is ‘pure’ is in question: with Akinetopsia come severe difficulties in obtaining structure from motion (Rizzo, Nawrot, Zihl, 1995). V5/hMT+ has since been implicated in this function (Grunewald, Bradley & Andersen, 2002) as well as determining depth (DeAngelis, Cumming and Newsome, 1998). Thus the current evidence suggests that motion processing occurs in a modular stream, although with a role in form and depth perception at higher levels.
| Methodology | Finding | Source |
|---|---|---|
| Physiology Physiology Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or... (single cell recording) |
Cells directionally and speed selective in MT/V5 | Zeki 1974; Van Essen et al. 1981; Maunsell & Van Essen 1983; Felleman & Kaas 1984 |
| Neuroimaging Neuroimaging Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain... |
Greater activation for motion information than static information in V5/MT | Buchel et al., 1998; Culham et al., 1998 ; Stiers et al., 2006 |
| Electrical-stimulation & perceptual | Following electrical stimulation of V5/MT cells perceptual decisions are biased towards the stimulated neuron’s direction preference | Salzman et al., 1992 |
| Magnetic-stimulation | Motion perception is also briefly impaired in humans by a strong magnetic pulse over the corresponding scalp region to hMT+ | Hotson et al., 1994; Beckers and Zeki, 1995; Walsh and Cowey., 1998 |
| Psychophysics Psychophysics Psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions they effect. Psychophysics has been described as "the scientific study of the relation between stimulus and sensation" or, more completely, as "the analysis of perceptual... |
Perceptual asynchrony among motion, color and orientation. | Moutoussis and Zeki (1997); Viviani & Aymoz (2001) |
| Methodology | Finding | Source |
|---|---|---|
| Physiology Physiology Physiology is the science of the function of living systems. This includes how organisms, organ systems, organs, cells, and bio-molecules carry out the chemical or physical functions that exist in a living system. The highest honor awarded in physiology is the Nobel Prize in Physiology or... (single cell recording) |
Complex motion involving contraction/expansion and rotation found to activate neurons in medial superior temporal area (MST) | Tanaka and Saito, 1989 |
| Neuroimaging Neuroimaging Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain... |
Biological motion activated superior temporal sulcus | Grossman et al., 2000 |
| Neuroimaging Neuroimaging Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain... |
Tool Tool A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such... use activated middle temporal gyrus and inferior temporal sulcus |
Beauchamp, Lee, Haxby and Martin, 2003 |
| Neuropsychology Neuropsychology Neuropsychology studies the structure and function of the brain related to specific psychological processes and behaviors. The term neuropsychology has been applied to lesion studies in humans and animals. It has also been applied to efforts to record electrical activity from individual cells in... |
Damage to visual area V5 results in akinetopsia |
Color processing
Similar converging evidence suggests modularity for color. Beginning with Gowers’ (1888) finding that damage to the fusiform/lingual gyri in occipitotemporal cortex correlates with a loss in color perception (achromatopsiaAchromatopsia
Achromatopsia , is a medical syndrome that exhibits symptoms relating to at least five separate individual disorders. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to an autosomal recessive congenital color vision disorder,...
) the notion of a "color centre" in the primate brain has had growing support (e.g. Meadows, 1974; Sacks and Wasserman, 1987; Zeki, 1990; Grüsser and Landis, 1991). Again, such clinical evidence only implicates that this region is critical to color perception
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
and nothing more. Other evidence, however, including neuroimaging
Neuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
and physiology (Wachtler et al. 2003; Kusunoki, Moutoussis & Zeki, 2006) converges on V4 as necessary to color perception. A recent meta-analysis
Meta-analysis
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. In its simplest form, this is normally by identification of a common measure of effect size, for which a weighted average might be the output of a meta-analyses. Here the...
has also shown a specific lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
common to achromats corresponding to V4 (Bouvier and Engel, 2006). From another direction altogether it has been found that when synaesthetes
Synesthesia
Synesthesia , from the ancient Greek , "together," and , "sensation," is a neurologically based condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway...
experience color by a non-visual stimulus V4 is active (Rich et al., 2006; Sperling et al., 2006). On the basis of this evidence it would seem that color processing is modular. However, as with motion processing it is likely that this conclusion is inaccurate. Other evidence shown in Table 3 implicates different areas’ involvement with color. It may thus be more instructive to consider a multistage color processing stream from the retina through to cortical areas including at least V1, V2, V4, PITd and TEO. Consonant with motion perception there appear to be a constellation of areas drawn upon for color perception. In addition, V4 may have a special but not exclusive role. For example, single cell recording has shown only V4 cells respond to the color of a stimuli rather than its waveband, whereas other areas involved with color do not (Wachtler et al. 2003; Kusunoki, Moutoussis & Zeki, 2006).
| Other areas involved with color/Other functions of V4 | Source |
|---|---|
| Wavelength Wavelength In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a... sensitive cells in V1 and V2 |
Livingstone & Hubel, (1984); DeYoe & Van Essen, (1985) |
| anterior parts of the inferior temporal cortex | Zeki & Marini, (1998); Beauchamp et al., (2000) |
| posterior parts of the superior temporal sulcus (PITd) | Conway & Tsao, (2006) |
| Area in or near TEO | Tootell, Nelissen Vanduffel Orban, (2004) |
| Shape detection | Pasupathy, (2006); David, Hayden, Gallant, (2006) |
| Link between vision Visual perception Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision... , attention Attention Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience.... and cognition Cognition In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science... |
Chelazzi, Miller, Duncan, & Desimone (2001) |
Form processing
Another clinical case that would a priori suggest a module for modularity in visual processing is visual agnosiaAgnosia
Agnosia is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss...
. The well studied patient DF is unable to recognize or discriminate objects (Mishkin, Ungerleider and Macko, 1983) owing to damage in areas of the lateral occipital cortex (James et al., 2003) although she can see scenes without problem – she can literally see the forest but not the trees (Steeves et al. 2006). Neuroimaging
Neuroimaging
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the brain...
of intact individuals reveals strong occipito-temporal activation during object presentation and greater activation still for object recognition (see Grill-Spector, 2003). Of course, such activation could be due to other processes, such as visual attention. However, other evidence that shows a tight coupling of perceptual and physiological changes (Sheinberg and Logothetis, 2001) suggests activation in this area does underpin object recognition. Within these regions are more specialized areas for face or fine grained analysis (Gauthier, Skudlarski, Gore and Anderson, 2000), place perception (Epstein & Kanwisher, 1998) and human body perception (Downing, Jiang, Shuman and Kanwisher, 2001). Perhaps some of the strongest evidence for the modular nature of these processing systems is the double dissociation between object- and face (prosop-) agnosia (e.g. Moscowitch, Winocur and Behrmann, 1997). However, as with color and motion, early areas (see Pasupathy, 2006 for a comprehensive review) are implicated too lending support to the idea of a multistage stream terminating in the inferotemporal cortex rather than an isolated module.
Functional modularity
One of the first uses of the term "module" or "modularity" occurs in the influential book "Modularity of MindModularity of mind
Modularity of mind is the notion that a mind may, at least in part, be composed of separate innate structures which have established evolutionarily developed functional purposes...
" by philosopher Jerry Fodor
Jerry Fodor
Jerry Alan Fodor is an American philosopher and cognitive scientist. He holds the position of State of New Jersey Professor of Philosophy at Rutgers University and is the author of many works in the fields of philosophy of mind and cognitive science, in which he has laid the groundwork for the...
(1983). A detailed application of this idea to the case of vision was published by Pylyshyn (1999), who argued that there is a significant part of vision that is not responsive to beliefs and is "cognitively impenetrable."
Much of the confusion concerning modularity exists in neuroscience because there is evidence for specific areas (e.g. V4 or V5/hMT+) and the concomitant behavioral deficits following brain insult (thus taken as evidence for modularity). In addition, evidence shows other areas are involved and that these areas subserve processing of multiple properties (e.g. V1: see Leventhal et al., 1995) (thus taken as evidence against modularity). That these streams have the same implementation in early visual areas, like V1 is not inconsistent with a modular viewpoint: to adopt the canonical analogy in cognition, it is possible for different software to run on the same hardware. A consideration of psychophysics
Psychophysics
Psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions they effect. Psychophysics has been described as "the scientific study of the relation between stimulus and sensation" or, more completely, as "the analysis of perceptual...
and neuropsychological data would suggest support for this. For example, psychophysics has shown that percepts for different properties are realized asynchronously (Moutoussis & Zeki 1997, Viviani & Aymoz, 2001). In addition, although achromats experience other cognitive defects (Gegenfurtner, 2003) they do not have motion or form deficits when their lesion is restricted to V4 (Zeki, 2005). Relatedly, Zihl and colleagues’ (1983) Akinetopsia
Akinetopsia
Akinetopsia, also known as cerebral akinetopsia or motion blindness, is an extremely rare neuropsychological disorder in which a patient cannot perceive motion in their visual field, despite being able to see stationary objects without issue. For patients with akinetopsia, the world becomes devoid...
patient shows no deficit to color or object perception (although deriving depth and structure from motion is problematic, see above) and object agnostics do not have damaged motion or color perception, making the three disorders triply dissociable. Taken together this evidence suggests that even though distinct properties may employ the same early visual areas they are functionally independent. Furthermore, that the intensity of subjective perceptual experience (e.g. color) correlates with activity in these specific areas (e.g. V4) (Bartels and Zeki, 2005), the recent evidence that synaesthetes
Synesthesia
Synesthesia , from the ancient Greek , "together," and , "sensation," is a neurologically based condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway...
show V4 activation during the perceptual experience of color, as well as the fact that damage to these areas results in concomitant behavioral deficits (the processing may be occurring but perceivers do not have access to the information) are all evidence for visual modularity.
See also
- HeautoscopyHeautoscopyHeautoscopy is a term used in psychiatry and neurology for the reduplicative hallucination of "seeing one's own body at a distance" . It can occur as a symptom in schizophrenia and epilepsy. Heautoscopy is considered as one possible explanation for the doppelgänger phenomena....
- ModularityModularityModularity is a general systems concept, typically defined as a continuum describing the degree to which a system’s components may be separated and recombined. It refers to both the tightness of coupling between components, and the degree to which the “rules” of the system architecture enable the...
- Society of MindSociety of MindThe Society of Mind is both the title of a book and the name of a theory of natural intelligence as written and developed by Marvin Minsky.-Minsky's model:...
which proposes the mind is made up of agents - Two Streams hypothesisTwo Streams hypothesisThe two-streams hypothesis is a widely accepted, but still controversial, account of visual processing. As visual information exits the occipital lobe, it follows two main channels, or "streams". The ventral stream travels to the temporal lobe and is involved with object identification...