Anatomical and physiological observations in monkeys indicate that the primate visual system consists of several separate and independent subdivisions that analyze different aspects of the same retinal image: cells in cortical visual areas 1 and 2 and higher visual areas are segregated into three interdigitating subdivisions that differ in their selectivity for color, stereopsis, movement, and orientation. The pathways selective for form and color seem to be derived mainly from the parvocellular geniculate subdivisions, the depth- and movement-selective components from the magnocellular. At lower levels, in the retina and in the geniculate, cells in these two subdivisions differ in their color selectivity, contrast sensitivity, temporal properties, and spatial resolution. These major differences in the properties of cells at lower levels in each of the subdivisions led to the prediction that different visual functions, such as color, depth, movement, and form perception, should exhibit corresponding differences. Human perceptual experiments are remarkably consistent with these predictions. Moreover, perceptual experiments can be designed to ask which subdivisions of the system are responsible for particular visual abilities, such as figure/ground discrimination or perception of depth from perspective or relative movement--functions that might be difficult to deduce from single-cell response properties.

https://science.sciencemag.org/content/sci/240/4853/740.full.pdf

Segregation of form, color, movement, and depth: anatomy, physiology, and perception

We have used positron emission tomography (PET), which measures regional cerebral blood flow (rCBF), to demonstrate directly the specialization of function in the normal human visual cortex. A novel technique, statistical parametric mapping, was used to detect foci of significant change in cerebral blood flow within the prestriate cortex, in order to localize those parts involved in the perception of color and visual motion. For color, we stimulated the subjects with a multicolored abstract display containing no recognizable objects (Land color Mondrian) and contrasted the resulting blood flow maps with those obtained when subjects viewed an identical display consisting of equiluminous shades of gray. The comparison identified a unique area (area V4) located in the lingual and fusiform gyri of the prestriate cortex. For motion, blood flow maps when subjects viewed moving or stationary black and white random-square patterns were contrasted. The comparison identified a unique area located in the region of the temporo-parieto-occipital junction (area V5). We thus provide direct evidence to show that, just as in the macaque monkey, different areas of the human prestriate visual cortex are specialized for different attributes of vision. The striate cortex (V1) and the contiguous visual area (V2), which in the monkey brain feed both the homologous areas, were active in all 4 conditions. This pattern of activity allowed us to use an extension of the approach to assess the functional relationship between the 3 areas during color and motion stimulation. This is based on an hypothesis-led analysis of the covariance structure of the blood flow maps and promises to be a powerful tool for inferring anatomical pathways in the normal human brain.(ABSTRACT TRUNCATED AT 250 WORDS)

https://www.jneurosci.org/content/jneuro/11/3/641.full.pdf

A direct demonstration of functional specialization in human visual cortex

Positron emission tomography (PET) was used to identify the neural systems involved in discriminating the shape, color, and speed of a visual stimulus under conditions of selective and divided attention. Psychophysical evidence indicated that the sensitivity for discriminating subtle stimulus changes in a same-different matching task was higher when subjects selectively attended to one attribute than when they divided attention among the attributes. PET measurements of brain activity indicated that modulations of extrastriate visual activity were primarily produced by task conditions of selective attention. Attention to speed activated a region in the left inferior parietal lobule. Attention to color activated a region in the collateral sulcus and dorsolateral occipital cortex, while attention to shape activated collateral sulcus (similarly to color), fusiform and parahippocampal gyri, and temporal cortex along the superior temporal sulcus. Outside the visual system, selective and divided attention activated nonoverlapping sets of brain regions. Selective conditions activated globus pallidus, caudate nucleus, lateral orbitofrontal cortex, posterior thalamus/colliculus, and insular-premotor regions, while the divided condition activated the anterior cingulate and dorsolateral prefrontal cortex. The results in the visual system demonstrate that selective attention to different features modulates activity in distinct regions of extrastriate cortex that appear to be specialized for processing the selected feature. The disjoint pattern of activations in extravisual brain regions during selective- and divided-attention conditions also suggests that preceptual judgements involve different neural systems, depending on attentional strategies.

https://www.jneurosci.org/content/jneuro/11/8/2383.full.pdf

Selective and divided attention during visual discriminations of shape, color, and speed: functional anatomy by positron emission tomography

1. The activity of single neurons was recorded in Macaca mulatta monkeys while they performed tasks requiring them to select a cued stimulus from an array of three to eight stimuli and report the orientation of that stimulus. Stimuli were presented in a circular array centered on the fixation target and scaled to place a single stimulus element within the receptive field of the neuron under study. The timing of the cuing event permitted the directing of visual attention to the spatial location of the correct stimulus before its presentation. 2. The effects of focal attention were examined in cortical visual areas V1, V2, and V4, where a total of 672 neurons were isolated with complete studies obtained for 94 V1, 74 V2, and 74 V4 neurons with receptive-field center eccentricities in the range 1.8-8 degrees. Under certain conditions, directed focal attention results in changes in the response of V1, V2, and V4 neurons to otherwise identical stimuli at spatially specific locations. 3. More than one-third of the neurons in each area displayed differential sensitivity when attention was directed toward versus away from the spatial location of the receptive field just before and during stimulus presentation. Both relative increases and decreases in neural activity were observed in association with attention directed at receptive-field stimuli. 4. The presence of multiple competing stimuli in the visual field was a major factor determining the presence or absence of differential sensitivity. About two-thirds of the neurons that were differentially sensitive to the attending condition in the presence of competing stimuli were not differentially sensitive when single stimuli were presented in control studies. For V1 and V2 neurons the presence of only a few (3-4) competing stimuli was sufficient for a majority of the neurons studied; a majority of the V4 neurons required six to eight stimuli in the array before significant differences between attending conditions occurred. 5. For V1 and V2 neurons the neuronal sensitivity differences between attending conditions were observed primarily at or near the peak of the orientation tuning sensitivity for each neuron; the differences were evident over a broader range of orientations in V4 neurons. 6. In conclusion, neural correlates of focal attentive processes can be observed in visual cortical processing in areas V1 and V2 as well as area V4 under conditions that require stimulus feature analysis and selective spatial processing within a field of competing stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Focal attention produces spatially selective processing in visual cortical areas V1, V2, and V4 in the presence of competing stimuli.

The analysis of moving visual patterns

: The mechanisms underlying effects of ionizing radiation on visual-motor tasks in combat are not understood but definitely involve some disruption of visual perception. The degree of involvement is not known and must be studied and quantified in animal models. It is possible to identify those parts of the central nervous system necessary for visual perception. Once these areas have been identified, their sensitivity to irradiation can be studied more precisely. Visual responses of area 18 neurons were studied in the awake, behaving monkey. Cells were divided into six different classes on the basis of their stimulus preferences and spatial characteristics. Orientation cells were sensitive to the orientation of elongated stimuli. Color cells had nonoriented receptive fields with spatially coextensive opponent color inputs. Direction cells preferred moving stimuli, giving the greatest response to movement in some direction and no response or inhibition to movement in the opposite direction. Spot cells preferred a properly positioned small spot of light and responded equally well to all directions of stimulus movement. Border cells responded best to a stimulus that filled an excitatory region without encroaching on a powerful suppressive flank. Lightinhibited cells had high maintained spontaneous activity that was reduced or abolished by light.

Visual responses of area 18 neurons in awake, behaving monkey.

Neurons in the superior colliculus, striate cortex, frontal eye fields, and posterior parietal cortex of the monkey respond to visual stimuli. Many of these cells discharge more intensely to a stimulus when it is to be the target for a saccadic eye movement than when fixation is maintained. We have demonstrated that such enhancement of the visual response is also present for cells in prestriate cortex. The prestriate effect is a modulation of the visual response and not a concomitant of oculomotor activity. It is present for eye movements away from as well as into the visual receptive field and is thus similar to that seen in striate cortex and different from that studied in the superior colliculus, frontal eye fields, and posterior parietal cortex. The visual responses of many prestriate cells habituate with repeated stimulation. When the monkey makes saccadic eye movements to a stimulus that is eliciting only a habituated response, the enhancement acts as a dishabituation which persists throughout the eye movement trials.

Behavioral enhancement of visual responses of prestriate neurons of the rhesus monkey.

The mechanisms underlying effects of ionizing radiation on visual-motor tasks in combat are not understood but definitely involve some disruption of visual perception. The degree of involvement is not known and must be studied and quantified in animal models. It is possible to identify those parts of the central nervous system necessary for visual perception. Once these areas have been identified, their sensitivity to irradiation can be studied more precisely. Visual responses of area 18 neurons were studied in the awake, behaving monkey. Cells were divided into six different classes on the basis of their stimulus preferences and spatial characteristics. Orientation cells were sensitive to the orientation of elongated stimuli. Color cells had nonoriented receptive fields with spatially coextensive opponent color inputs. Direction cells preferred moving stimuli, giving the greatest response to movement in some direction and no response or inhibition to movement in the opposite direction. Spot cells preferred a properly positioned small spot of light and responded equally well to all directions of stimulus movement. Border cells responded best to a stimulus that filled an excitatory region without encroaching on a powerful suppressive flank. Lightinhibited cells had high maintained spontaneous activity that was reduced or abolished by light.

Visual responses of area 18 neurons in the awake, behaving monkey. Scientific report

http://link.springer.com/content/pdf/10.1007/978-3-642-81055-8_76.pdf

D. L. Robinson

Papers

Visual responses of area 18 neurons in awake, behaving monkey.

Behavioral enhancement of visual responses of prestriate neurons of the rhesus monkey.

Visual responses of area 18 neurons in the awake, behaving monkey. Scientific report

Functional Organization of Area 18 in the Rhesus Monkey