The interaction between surface color and color knowledge: behavioral and electrophysiological evidence

In this study, we used event-related potentials (ERPs) to evaluate the contribution of surface color and color knowledge information in object identification. We constructed two color-object verification tasks - a surface and a knowledge verification task - using high color diagnostic objects; both typical and atypical color versions of the same object were presented. Continuous electroencephalogram was recorded from 26 subjects. A cluster randomization procedure was used to explore the differences between typical and atypical color objects in each task. In the color knowledge task, we found two significant clusters that were consistent with the N350 and late positive complex (LPC) effects. Atypical color objects elicited more negative ERPs compared to typical color objects. The color effect found in the N350 time window suggests that surface color is an important cue that facilitates the selection of a stored object representation from long-term memory. Moreover, the observed LPC effect suggests that surface color activates associated semantic knowledge about the object, including color knowledge representations. We did not find any significant differences between typical and atypical color objects in the surface color verification task, which indicates that there is little contribution of color knowledge to resolve the surface color verification. Our main results suggest that surface color is an important visual cue that triggers color knowledge, thereby facilitating object identification.     

Illusory bands in orientation and spatial frequency: a cortical analog to Mach bands

Illusory bands at a luminance transition in space (ie an edge) are well known. Here we demonstrate illusory bands of enhanced orientations or spatial frequencies at transitions between higher-contrast and lower-contrast image content along the orientation and spatial-frequency dimensions--the dimensions of cortical spatial coding. We conclude that this illusion is a consequence of cortical-level suppression of units of similar orientations and spatial frequencies and serves to aid texture segmentation while providing efficient neural coding.     

Mechanisms of percept-percept and image-percept integration in vision: behavioral and electrophysiological evidence

Previous research has shown that the detection of a visual target can be guided not only by the temporal integration of two percepts, but also by integrating a percept and an image held in working memory. Behavioral and event-related brain potential (ERP) measures were obtained in a target detection task that required temporal integration of 2 successively presented stimuli in the left or right hemifield. Task performance was good when both displays followed each other immediately (percept-percept integration) and when displays were separated by a 300- or 900-ms interval (image-percept integration), but was poor with intermediate interstimulus intervals. An enhanced posterior negativity at electrodes contralateral to the side of the target was observed for percept-percept and for image-percept integration, demonstrating that both are based on spatiotopic representations. However, this contralateral negativity emerged later and was more sustained on trials with long interstimulus intervals, indicating that image-percept integration is slower and involves a sustained activation of working memory.     

Fast color grouping and slow color inhibition: evidence for distinct temporal windows for separate processes in preview search

The authors report 4 experiments that examined color grouping and negative carryover effects in preview search via a probe detection task (J. J. Braithwaite, G. W. Humphreys, & J. Hodsoll, 2003). In Experiment 1, there was evidence of a negative color carryover from the preview to new items, using both search and probe detection measures. There was also a negative bias against probes on old items that carried the majority color in the preview. With a short preview duration (150 ms) carryover effects to new items were greatly reduced, but probe detection remained biased against the majority color in the old items. Experiments 2 and 4 showed that the color bias effects on old items could be reduced when these items had to be prioritized relative to being ignored. Experiment 3 tested and rejected the idea that variations in the probability of whether minority or majority colors were probed were crucial. These results show that the time course of color carryover effects can be separated from effects of early color grouping in the preview display: Color grouping is fast, and inhibitory color carryover effects are slow.     

Visual change with moving displays: more evidence for color feature map inhibition during preview search

Preview search with moving stimuli was investigated. The stimuli moved in multiple directions, and preview items could change either their color or their shape before onset of the new (search) displays. In Experiments 1 and 2, the authors found that (a) a preview benefit occurred even when more than 5 moving items had to be ignored, and (b) color change, but not shape change, disrupted preview search in moving stimuli. In contrast, shape change, but not color change, disrupted preview search in static stimuli (Experiments 3 and 4). Results suggest that preview search with moving displays is influenced by inhibition of a color map, whereas preview search with static displays is influenced by inhibition of locations of old distractors.     

Spatial location in color vision

Ross argues that the location problem for color-the problem of how it is represented as occupying a particular location in space-constitutes an objection to color subjectivism. There are two ways in which the location problem can be interpreted. First, it can be read as a why-question about the relation of visual experience to the environment represented: Why does visual experience represent a patch of color as located in this part of space rather than that? On this interpretation, the subjectivist can answer Ross's objection by appealing to the physical location of reflectance rather than color. Second, it can be read as a how-question about visual representation itself: How does visual experience put together the experience of a color with the experience of its being located in space? This version makes the location problem a problem about visual experience itself and renders the ontology of color irrelevant to its solution. The location problem is thus no more a problem for the color subjectivist than for the color realist.     

The structure of three-dimensional object representations in human vision: evidence from whole-part matching

This article examines how the human visual system represents the shapes of 3-dimensional (3D) objects. One long-standing hypothesis is that object shapes are represented in terms of volumetric component parts and their spatial configuration. This hypothesis is examined in 3 experiments using a whole-part matching paradigm in which participants match object parts to whole novel 3D object shapes. Experiments 1 and 2, consistent with volumetric image segmentation, show that whole-part matching is faster for volumetric component parts than for either open or closed nonvolumetric regions of edge contour. However, the results of Experiment 3 show that an equivalent advantage is found for bounded regions of edge contour that correspond to object surfaces. The results are interpreted in terms of a surface-based model of 3D shape representation, which proposes edge-bounded 2-dimensional polygons as basic primitives of surface shape.     

Computation of cone contrasts for color vision research

Cone-contrast coordinates have proved useful for representing transient test stimuli used in color vision experiments. These representations automatically take into account the spectral absorption of cones and any Weberian adaptation to steady fields of light. Under these conditions, they also can be interpreted as being an approximation to the incremental cone response. A detailed methodology is presented for making appropriate measurements and calculations of cons contrasts for any light source, especially color monitors.     

Qualities of color vision in infancy.

Four-month-old infants attended differentially to eight equally bright, monochromatic spectral lights; that is, they discriminated colors. Moreover, infants showed the same pattern of differential attention regardless of experimental group (different groups of infants saw different subsets of all possible pairings of colors) or experimental method (paired comparisons or single stimulus). In general, the differential attention of infants to colors parallels the ratings of the pleasantness of those same colors by adults. Finally, infants looked significantly longer at color category centers than at color category boundaries. These results suggest that looking at this early stage of infancy can better be understood in terms of preference rather than in terms of stimulus categorization. The results also provide further evidence for a neural excitation model of early visual attention.     

The role of color in high-level vision

Traditional theories of object recognition have emphasized the role of shape information in high-level vision. However, the accumulating behavioral, neuroimaging and neuropsychological evidence indicates that the surface color of an object affects its recognition. In this article, we discuss the research that examines the conditions under which color influences the operations of high-level vision and the neural substrates that might mediate these operations. The relationship between object color and object recognition is summarized in the 'Shape+Surface' model of high-level vision.     

Somatic responses in behavioral inhibition

In the present study, skin conductance responses (SCRs) were measured postdecision and prefeedback in a go/no-go (GNG) task in which participants used response feedback to learn when to respond or not to respond to numeric stimuli. Like somatic markers in gambling tasks and somatic reactions to error monitoring in choice reaction time tasks, SCR patterns distinguished between correct and incorrect trials over time. These somatic reactions were disrupted by a reversal of GNG contingencies, and they were facilitated by pretraining of the stimulus—response mappings. In all cases, however, the somatic reactions appeared to be a product of competent decision making rather than a contributor to performance. Differential somatic responses to good and bad choices appear to be a robust and fairly general phenomenon, but researchers should be cautious in assuming that the somatic responses contribute to performance.     

Prioritized selection in visual search through onset capture and color inhibition: evidence from a probe-dot detection task

Observers performed a preview search task in which, on some trials, they had to indicate the presence of a briefly presented probe-dot. Probes could be presented on locations corresponding to old or new elements and prior to or after the presentation of the new elements. After the presentation of the new elements, probes were generally detected faster on new than on old locations, indicating prioritized selection of new elements. Prior to the presentation of the new elements, probes were detected faster on new than on old locations only when old and new elements differed in color. These results suggest that prioritized selection of new elements is mediated not by visual marking but by onset capture. Additionally, observers may apply color-based inhibition.     

Masked inhibitory priming in english: evidence for lexical inhibition

Predictions derived from the interactive activation (IA) model were tested in 3 experiments using the masked priming technique in the lexical decision task. Experiment 1 showed a strong effect of prime lexicality: Classifications of target words were facilitated by orthographically related nonword primes (relative to unrelated nonword primes) but were inhibited by orthographically related word primes (relative to unrelated word primes). Experiment 2 confirmed IA's prediction that inhibitory priming effects are greater when the prime and target share a neighbor. Experiment 3 showed a minimal effect of target word neighborhood size (N) on inhibitory priming but a trend toward greater inhibition when nonword foils were high-N than when they were low-N. Simulations of 3 different versions of the IA model showed that the best fit to the data is produced when lexical inhibition is selective and when masking leads to reset of letter activities.