Inhibitory interaction between channels sensitive to direction and velocity in the human visual system

Two paradigms for the study of velocity contrast have been employed. Paradigm one has focused on perceived velocity changes across a field. Paradigm two has focused on perceived velocity changes at the juncture of disparate velocities. The current experiments employ both paradigms to look at oppositely directed motion. Using paradigm two, it was determined that, with oppositely directed motion, the effect on perceived velocity could not be attributed to lateral inhibitory interaction--in contrast to earlier reports of lateral interaction when motion was in the same direction. Using paradigm one, it was determined that the effect upon perceived velocity with oppositely directed motion appeared to involve inhibition across entire fields of motion.     

Two channels for flicker in the human visual system

The human visual system contains a large number of narrowly-tuned spatial-frequency-specific channels. Does it contain an analogous set of channels tuned to a narrow range of temporal frequency? On the basis of data gathered with the use of a threshold elevation technique it is argued that human sensitivity to flicker can be accounted for by assuming the existence of just two filters, one a low-pass filter peaking gently at around 6 Hz and one a band-pass filter peaking at around 9 Hz. Similar data gathered from studies of interocular transfer suggest that at least some of the mechanisms involved are binocular, rather than being purely monocular as has previously been suggested.     

Relationship between visual orientation and susceptibility to motion sickness.

24 male subjects were divided into 3 groups, on the basis of their susceptibility to motion sickness. All subjects were then required to set a luminous line in an apparently vertical position while viewing the line from a body position which was deviated 70 degrees laterally from the upright. No visible frame of reference was available. A significant relationship between motion sickness susceptibility and errors in judging the vertical was discovered, the "intermediate" susceptibility group making the greatest errors. The role of the vestibular system in visual orientation and motion sickness is discussed. The result also indicates the potential value of using perceptual performance as a tool in the study of motion sickness and its correlates.     

Interactions between visual working memory and selective attention

The relationship between working memory and selective attention has traditionally been discussed as operating in one direction: Attention filters incoming information, allowing only relevant information into short-term processing stores. This study tested the prediction that the contents of visual working memory also influence the guidance of selective attention. Participants held a sample object in working memory on each trial. Two objects, one matching the sample and the other novel, were then presented simultaneously. As measured by a probe task, attention shifted to the object matching the sample. This effect generalized across object type, attentional-probe task, and working memory task. In contrast, a matched task with no memory requirement showed the opposite pattern, demonstrating that this effect is not simply due to exposure to the sample. These results confirm a specific prediction about the influence of working memory contents on the guidance of attention.     

Identification of temporal coherence between auditory and visual channels

Attention, Perception, & Psychophysics - The accuracy of identification of the temporal coherence between auditory and visual channels was examined. Random sequences of sound and light bursts...     

Orientational anisotropy in the human visual system

When a target stimulus in a predesignated location is identified by a keypress response, responses are slightly faster if noise stimuli in adjacent locations are identical to the target than if they are a different stimulus assigned to the same response (a repeated-stimulus superiority effect). An exception to this result has been found in experiments that used randomly intermixed letter and digit stimuli. These experiments showed slower responding for identical noise than for nonidentical, response-compatible noise (a repeated-stimulus inferiority effect). The present study investigated these phenomena in three experiments. Experiments 1 and 2 established that both the superiority and inferiority effects can be obtained in the same experiment. They also provided evidence that the repeated-stimulus inferiority effect is a function of the intermixing of letters and digits and not of the larger target-set size that has been used for mixed lists. Experiment 3 demonstrated that, with unmixed presentation, the repeated-stimulus superiority effect is enhanced by an increase in the number of stimuli assigned to each response. The experiments are consistent with accounts that attribute the repeated-stimulus superiority effect to competition that occurs when different internal recognition responses are activated. Moreover, the experiments suggest that the repeated-stimulus inferiority effect has its basis in processes that occur subsequent to feature extraction.     

Representational content and computation in the human visual system

Summary Information-processing systems can be characterized by their ability to transform systematically certain internal representational states (symbols) into one another. The presence of such an information-processing capacity calls for an explanation. How could such an explanation in principle be formulated? How is it possible to specify internal representational states and to ascribe to them certain representational contents? What has to be demonstrated by such explanations is how an information-processing capacity is actually instantiated in a system. In this paper, the outlines of an explanation by instantiation are sketched for a specific human visual capacity. In addition, some fundamental problems facing the development of this explanation will be discussed.     

The relationship between central cues and peripheral cues in covert visual orientation

Four experiments were conducted to compare valid and invalid cue conditions for peripheral and central cues. Experiments 1, 3, and 4 used reaction time (RT) as the dependent variable. Experiment 2 used a threshold measure. Peripheral and central cues were presented on each trial. The peripheral cue was uninformative in all experiments. The central cue was informative in Experiments 1 and 2, where it predicted stimulus side on 70% of the trials. Experiment 3 included 50% and 100% central-cue prediction conditions as well as the 70% treatment. Experiment 4 included 60%, 75%, and 90% central-cue prediction conditions. The effects of the central and peripheral cues were independent and additive in all four experiments, indicating that: (1) both cue types can act simultaneously, and that the relationship between them is additive under the conditions used in these experiments, (2) informativeness is not a necessary condition for attentional effects with peripheral cues, and (3) covert visual orientation influences sensory thresholds and RT in similar ways. The results of Experiments 3 and 4 demonstrated that the facilitation associated with peripheral cues was insensitive to manipulations which demonstrate that subjects use the informational value of the central cue to direct voluntary attention. The results are discussed with reference to two issues; first, the proposition that central and peripheral cues exert their influence on performance in independent information-processing stages, following the additive factor method, and, second, the problems raised for additive factors method when cues elicit both an “explicit” response—regarding the presence or absence of a specified letter—and an “implicit response”—involving the planning and possible execution of eye and hand movements.     

Spatiotemporal isosensitivity fields in the human visual system

The human visual system is capable of detecting correlations, manifested perceptually as global pattern, in mathematically constrained dynamic textures. This ability has given rise to speculation that correlative mechanisms in the human visual system exist and that they have a neural basis similar to the orientationally selective structures discovered in area 17 of the mammalian visual cortex. The limits to the detection of correlation were mapped, spatially and temporally, by means of a psychophysical technique. Evidence is presented that, at least in the spatial domain, the correlation mechanism may be served by a population of such neural units.     

Perceptual depth synthesis in the visual system as revealed by selective adaptation

Selective adaptations was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients.     

Loss of wavelength selectivity in contour masking and aftereffect following dichoptic adaptation

Two experiments measured the apparent orientation (aftereffect) and the threshold for detection (masking) of a colored grating viewed by one eye after exposure to a colored grating to the same or the opposite eye (monoptic inspection) or after stimulation of one eye by color and the other eye by contours (dichoptic inspection). Under the monoptic condition, the color relationship between the inspection and test stimuli exerted control over the extent of aftereffect and masking when the two stimuli were viewed with the same eye, but not when they were seen with different eyes. Aftereffect and masking were nonselective to wavelength following dichoptic inspection, irrespective of whether the test stimulus was presented to the color-adapted or to the contour-adapted eye. The results support other claims that visual detectors with chromatic and spatial tuning have monocular specificity.     

Local and global orientation in visual search

Six experiments investigated the role of global (shape) and local (contour) orientation in visual search for an orientation target. Experiment 1 demonstrated thatsearch for a conjunction of local contours with a distinct global orientation was less efficient than search for a target featurally distinct in terms of both global and local contour orientation. However, Experiments 2 and 4 demonstrated that the presence of a unique line contour was neither sufficient nor necessary to allow efficient search. Experiment 5 found thatsearch for a local orientation difference was strongly impeded by irrelevant variation in global orientation, arguing for a preeminent role for global orientation. Finally, Experiment 6 demonstrated that the orientation search asymmetry holds for the global orientation of stimuli. Taken together, the results are consistent with visual search processes guided predominately by a representation of global orientation.     

Frequency specific chromatic adaptation in the human visual system

Subjects were exposed to a vertical chromatic grating alternating with horizontal chromatic grating of the identical frequency. They were then tested with a series of test gratings of varied spatial frequencies to examine whether the responses were effected by the spatial frequency of the adaptation pattern in relation to the test pattern. It was found that maximum response occurred when adaptation and test gratings had the same spatial frequency, the effect was asymmetric and finally that enhancements were found at octaves. Thus the experiment further demonstrated that neural elements specific to spatial frequency exist in the human visual system.