Stimulus suffixes and visual presentation.
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Form Perception↗
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Results for “Pattern Recognition, Visual”
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A word superiority effect with nonorthographic acronyms: testing for unitized visual codes.
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Cognition↗
[Temporal course of a so-called automatic visual attention process].
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Attention↗
Brain processing of optical input: the perception of visual reality.
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Adult↗
The role of expression and identity in the face-selective responses of neurons in the temporal visual cortex of the monkey.
Neurophysiological studies have shown that some neurons in the cortex in the superior temporal sulcus and the inferior temporal gyrus of macaque monkeys respond to faces. To determine if facial factors such as expression and identity are encoded independently by face-responsive neurons, 45 neurons were tested on a stimulus set depicting 3 monkeys with 3 expressions each. As tested on a two-way ANOVA, 15 neurons showed response differences to different identities independently of expression, and 9 neurons showed responses to different expressions independently of identity. Three neurons showed significant effects of both factors. Six of the neurons with responses related to expression responded primarily to calm faces, while 2 responded primarily to threat faces. Of a further set of 31 neurons tested on pairs of different expressions, 6 showed strong responses to open-mouth fear or threat expressions, while 2 showed stronger responses to calm faces than threat expressions. Neurons responsive to expression were found primarily in the cortex in the superior temporal sulcus, while neurons responsive to identity were found primarily in the inferior temporal gyrus. The difference in anatomical distribution was statistically significant. This supports the possibility that specific impairments of the recognition of the identity of a face and of its expression in man are due to damage to or disconnection of separate neuronal substrates.
Animals↗
Characteristics of perceptual grouping in rats.
Parametric analysis was made of the characteristics by which proximity and alignment serve as cues for perceptual grouping in rats. Rats were initially conditioned to discriminate a series of horizontal lines from vertical lines. Following training, rats were presented with test stimuli that consisted of bistable arrays of disjunct dots. A grouping cue (greater proximity, greater alignment, or both) was randomly assigned to either the horizontal or vertical orientation. The effectiveness of the cues was based on behavioral responses to the cued orientation. Results indicated that proximity served as a cue for perceptual grouping. The effectiveness of the proximity cue was less for rats than found previously in humans and, unlike humans, diminished with increased stimulus scale. Rats did not respond to alignment cues when used in isolation, although alignment facilitated grouping when used in conjunction with proximity cues. Diminished effectiveness of grouping cues likely reduces object recognition abilities, particularly for complex visual stimuli.
Animals↗
Event-related potentials to faces: the effects of priming and recognition.
Short-term visual memory, as in both implicit priming and explicit recognition tasks, can be demonstrated by decreased reaction times, the ability to preferentially select previously presented objects from lists and the ability to more readily complete previously exposed words from fragmented letters. The visual processing of faces occurs separately from the visual processing of non-face stimuli, within discrete areas of bilateral posterior inferotemporal cortices. While visual recognition and memory of faces are independent of those for non-faces, their processing appears to be similar. We have demonstrated an electrophysiologic correlate of short-term visual memory in a face-matching paradigm. We have observed a series of evoked potential components consisting predominantly of a C140, C180 and C240 with a posterior, bitemporal distribution. The priming effect is reflected by a diminution of C240 amplitude in the response to repeated pictures of faces compared to novel pictures of faces. These data reflect a previously unreported set of neurophysiological observations on short-term visual memory for faces.
Adult↗
Event-related potentials and information processing in infants with and without Down syndrome.
Event-related brain potentials (ERPs) were recorded from 6-month-old infants with and without Down syndrome presented with a visual recognition memory task. The ERP morphology was the same for both groups. The chronometry of information processing by infants with Down syndrome was similar to or faster than that of the infants without Down syndrome, depending on ERP component. The amplitude differences between groups may implicate frontal attentional processes in Down syndrome as opposed to more posterior processes. Infants with Down syndrome had an amplitude decrement in Nc over the central but not frontal cortex. The infants with Down syndrome also had similar visual fixation. Infants may have more subtle differences than those found in older individuals with Down syndrome.
Arousal↗
Recognition of positive and negative bandpass-filtered images.
A study is reported in which the significance for vision of low- and high-spatial-frequency components of photographic positive and negative images was investigated by measuring recognition of bandpass-filtered photographs of faces. The results show that a 1.5 octave bandpass-filtered image contains sufficient visual information for good recognition performance, provided the filter is centred close to 20 cycles facewidth-1. At low spatial frequencies negatives are more difficult to recognize than positives, but at high spatial frequencies there is no difference in recognition, implying that it is the low-frequency components of negatives which present difficulties for the visual system.
Color Perception↗
Absence of a hemispheric superiority in the recognition of European and Asian faces.
The present study was designed to examine whether there is a difference in hemispheric superiority in the recognition of European and Asian faces. A visual hemifield-presentation technique involving monocular testing was employed. Ten European subjects were presented a recognition task involving European faces and 10 other European subjects a similar task involving Asian faces. The data indicated no hemispheric superiority in either case; however, subjects made significantly more errors in recognising Asian faces than European faces in both visual hemifields.
Dominance, Cerebral↗
Normal strobe electroretinograms without pattern electroretinograms in albino rats.
Electroretinograms (ERGs) were obtained from pigmented and albino rats to step luminance changes of an unpatterned TV screen. Surround luminance was increased until the ERG became small and focal. In pigmented rats the ERG at on was positive, earlier, and about twice the amplitude of the negative ERG at off. All pigmented rats had pattern ERGs-0.5 cycles/deg in dark agouti rats and an octave less in hooded rats. Implicit peak times were similar to that of the sum of on plus off focal ERGs from the same animals (85 ms). In albino rats off responses were more like on. The resultant sum was consequently small. Both peak times were similar and did not move earlier than 120 ms as surround luminance increased. Pattern ERGs could not be recorded from albinos at any spatial frequency or surround luminance. These pigmented rat ERGs seem to have two major components. One follows luminance linearly; the other is a fully rectified nonlinearity with about one-third the amplitude. The albino rat retina apparently lacks the latter component. These deficiencies may occur in albinos of other species and be associated with their visual system abnormalities.
Albinism↗
Visual grouping without low spatial frequencies.
Gestalt psychologists have stressed the perceptual importance of grouping. On the basis of multichannel theory of early visual processing, grouping has been attributed to the operation of channels tuned to low spatial frequencies. If this explanation is correct and sufficient, grouping should not occur when looking at highpass filtered images, because they do not excite low spatial frequency channels. However this paper brings evidence that visual grouping also occurs in such a situation. Hence, a more comprehensive explanation of visual grouping is needed.
Filtration↗
Grating detection and identification: comparison of postadaptation reaction times.
The effect of pattern adaptation on grating detection and grating identification was investigated by the method of reaction time. The test and adapting stimuli were sinusoidal vertical gratings. Adaptation caused a spatial frequency-selective increase of the mean detection reaction times. However, the mean identification reaction times were delayed regardless of the adapting spatial frequency. The similarity of the present results with some data about visually evoked potentials is discussed.
Adaptation, Ocular↗
Universality in visual cortical pattern formation.
During ontogenetic development, the visual cortical circuitry is remodeled by activity-dependent mechanisms of synaptic plasticity. From a dynamical systems perspective this is a process of dynamic pattern formation. The emerging cortical network supports functional activity patterns that are used to guide the further improvement of the network's structure. In this picture, spontaneous symmetry breaking in the developmental dynamics of the cortical network underlies the emergence of cortical selectivities such as orientation preference. Here universal properties of this process depending only on basic biological symmetries of the cortical network are analyzed. In particular, we discuss the description of the development of orientation preference columns in terms of a dynamics of abstract order parameter fields, connect this description to the theory of Gaussian random fields, and show how the theory of Gaussian random fields can be used to obtain quantitative information on the generation and motion of pinwheels, in the two dimensional pattern of visual cortical orientation columns.
Animals↗
Shades of Déjerine--forging a causal link between the visual word form area and reading.
In 1892, the French neurologist Jules Déjerine suggested that pure alexia resulted from an occipital lesion that selectively disconnected visual input from a region of the brain that housed "optical images of words." In this issue of Neuron, Gaillard and colleagues offer evidence consistent with Déjerine's proposal and provide new insights to the functional role of the "visual word form area."
Alexia, Pure↗
Display symmetry affects positional specificity in same-different judgment of pairs of novel visual patterns.
Deciding whether a novel visual pattern is the same as or different from a previously seen reference is easier if both stimuli are presented to the same rather than to different locations in the field of view (Foster & Kahn (1985). Biological Cybernetics, 51, 305-312; Dill & Fahle (1998). Perception and Psychophysics, 60, 65-81). We investigated whether pattern symmetry interacts with the effect of translation. Patterns were small dot-clouds which could be mirror-symmetric or asymmetric. Translations were displacements of the visual pattern symmetrically across the fovea, either left-right or above-below. We found that same-different discriminations were worse (less accurate and slower) for translated patterns, to an extent which in general was not influenced by pattern symmetry, or pattern orientation, or direction of displacement. However, if the displaced pattern was a mirror image of the original one (along the trajectory of the displacement), then performance was largely invariant to translation. Both positional specificity and its reduction in symmetric displays may be explained by location-specific pre-processing of the visual input.
Adult↗
Perceived shape regularity does not depend on regularities along the contour.
In four experiments we investigated whether human observers are able to use certain regularities in polygons when they have to indicate which polygon they perceive as the more regular in a paired comparison task. From our results we conclude that regularities that are restricted to the contour do not play a role in judgments of regularity. For instance, equilateral polygons are not considered to be more regular than entirely random polygons. Only bilaterally symmetric polygons are consistently judged as regular. However, we show that this is caused by regularities across the polygon. These results are at odds with approaches that assume that regularities along the contour play an important part in visual perception.
Adult↗
Visual saliency and texture segregation without feature gradient.
A central notion in the study of texture segregation is that of feature gradient (or feature contrast). In orientation-based texture segregation, orientation gradients have indeed played a fundamental role in explaining behavioral results. Here, however, we show that general, smoothly varying, orientation-defined textures (ODTs) exhibit striking perceptual singularities that are completely unpredictable from orientation gradients. These singularities defy not only popular texture segregation theories but also virtually all computational segmentation methods, and they confound previous behavioral studies with smoothly varying ODTs. We provide psychophysical evidence that perceptual singularities in smooth ODTs are salient visual features consistent across observers and with significant effect on the perception and segregation of oriented textures. We further show that, although orientation gradients cannot predict them, perceptual singularities in smooth ODTs emerge directly from, and can be spatially localized by, two ODT curvatures. Given the traditional role of feature gradients in early vision, the significance of these findings extends well beyond orientation-based texture segregation to issues ranging from curve integration and fragment grouping, through the perception of 3D shape, to the functional organization of the primary visual cortex.
Depth Perception↗