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At least 1,693 records · Page 94Linked to original sources
PubMed1984

Macaque striate cortex: pattern, movement and colour processing.

Simple cells in the primate visual cortex provide a form of generalized, pre-cognitive mapping of visual scenes. One point in space is represented by several orientation-specific cells capable of signalling both standing contrast and contrast changes in the scene. The arrangement of simple receptive fields (with a few antagonistic subregions) suggest analysis of scenes both in terms of symmetrical and antisymmetrical spatial components (i.e. lines and edges) and spatial-frequency contents. There is no evidence that this analysis is carried out within fixed areas (or patches) since a diversity of receptive field sizes was observed. A chromatic content is probably analysed by a different class of cells with concentric, cone-opponent receptive fields.

Animals↗
PubMed1984

Dynamic topography of visual evoked potentials and extrageniculate projection in case of Riddoch phenomenon.

A 34-year-old woman showing the Riddoch phenomenon was studied by the technique of dynamic topography of visual evoked potential (VEP). This case had cortical blindness which developed during the process of massive intestinal hemorrhage, shock and surgery. The visual acuity was limited to hand movement, and perception of white and colored light was present, but there was no form recognition. Tracking eye movement for a flashlight was possible and optokinetic nystagmus (OKN) also appeared. CT-scan showed a diffuse low density area in the white matter of the occipital lobe. The VEPs by flash and a checkerboard of 60'-100' were detectable. Dynamic topography of the VEP showed that a strong negative deflection from the brainstem appeared at around 30 msec and this deflection expanded to the parietal region at about 90 msec. Subsequently, a positive deflection extending from the frontal region to the occipital region continued at 100 msec to 150 msec. Such a process of reaction is not observed in the normal subject. These findings suggest that the visual reaction was conducted abnormally through the extrageniculate system; from the brainstem to the parietal area and then to the occipital area.

Adult↗
PubMed1980

The feature-positive effect in adult human subjects.

Previous experiments with animals and young children have shown that discriminations based on the presence versus absence of a single feature are learned more easily when the feature appears on reinforced rather than nonreinforced displays. Six experiments demonstrated an analogous effect in college students, across a range of stimulus materials, general procedures, kinds of feedback, pacing of trials, and instructions to the subject. The results were analyzed in terms of the exceptionally strong control of behavior by events that are present on positive trials. These findings have implications for theoretical interpretations of human concept learning and decision making, and offer additional examples of the difficulty organisms experience in using "nonoccurrence" as a cue.

Concept Formation↗
PubMed1998

Cognitive channels computing action distance and direction.

Visually guided, goal-directed reaching requires encoding action distance and direction from attributes of visual landmarks. We identified a cognitive mechanism that seemingly performs visual motor extension before action initiation and replicated and extended previous results that identified a mechanism for visual motor mental rotation. We find that humans systematically delay action onset while newly planning increasingly distant arm movements beyond a visual landmark, consistent with an internal representation for visual motor extension. Onset times also changed systematically during concurrent mental rotation and visual motor extension computations required to process new directions and distances. Visual motor extension associated with reaching slowed when participants needed to plan action direction within the same time frame, whereas mental rotation efficiency was unaffected by concurrent needs to prepare action distance. In contrast to parallel direction and distance computations needed for direct aiming to a visual target, the planning of new directions and distances likely occurs at distinct times. When considered with previous findings, the current results suggest the existence of an intermediate component of motor preparation that engages a covert mechanism of cognitive motor planning.

Adolescent↗
PubMed2000

Attribution of meaning from movement of simple objects.

Many researchers claim that attribution of meaning to movement is based prevalently on the properties of the kinetic pattern. Using a constant kinetic pattern, the present study examined the possible influence of shape, size, luminance, and hue of the moving objects on the attribution of meaning. A significant influence of the shape and luminance of the moving objects on the expressivity of the kinetic pattern was found. This influence is probably due to the fact that the kinetic conditions were not unequivocal and specific and so easily influenced by some figural properties. The hue and size of the moving objects seemed instead to have little importance in the attribution of meaning to movement. The need for further investigation to assess the influence of the properties of the kinetic pattern on the perception of a mechanical, intentional, or expressive event is suggested.

Adolescent↗
PubMed1995

Apparent motion produced by temporally modulated brightness contrast and assimilation.

When regions containing a counterphasing sine-wave grating are presented side by side and in spatial and temporal quadrature phase, a transparent perception of motion results. This occurs even though none of the stimulus parts is moving. The two percepts of motion in these displays are in opposite directions, one analogous to brightness contrast, the other to brightness assimilation. If the regions are separated by a gap, the contrast and assimilation motions remain visible for separations up to 0.5 and 1 period, respectively. Both motions occur at temporal frequencies from 1 to 16 Hz. The perceived motion analogous to brightness assimilation is easily modeled with elongated receptive fields that integrate flux along the long axis, such as simple cells. The perceived motion analogous to brightness contrast can be accounted for by receptive fields that subtract the flux in one region from the flux in another region. Examples are center-surround subunits such as are found in the elaborated Reichart model [W. Reichardt, in Sensory Communication, W. A. Rosenblith, ed. (MIT Press, Cambridge, Mass., 1961), pp. 303-317; J. P. H. van Santen and G. Sperling, J. Opt. Soc. Am. A 2, 300-321 (1985)]. The dual perceived motion suggests that more than one kind of motion channel (distinguished by the two-dimensional receptive field of the front-end filter) is present in the human visual system.

Contrast Sensitivity↗
PubMed1985

Eye movements and stereopsis during dichoptic viewing of moving random-dot stereograms.

The dynamic properties of the version and vergence system were studied in relation to stereopsis for movements of the whole visual scene. Large random-dot stereograms (30 X 30 deg arc), moving laterally, were viewed dichoptically by human subjects without a fixed visual frame of reference. Sinusoidal movements in counterphase of the two half-images constituting the stereogram induced sinusoidal ocular vergence movements. The gain of vergence depended on the frequency as well as the amplitude of stimulus movement, while the phase lag depended only on the frequency. Fusion and stereopsis were retained up to a maximal velocity of change in relative position of the two half-images between 6 and 13.5 deg/sec. Sinusoidal movement of one half-image while the other one remained stationary induced sinusoidal ocular version as well as vergence movements. For version gains were higher and phase lags were smaller than for vergence. At the retinal level, residual overall binocular disparities between the two half-images up to 2 deg arc were tolerated without loss of stereopsis. The presence of sinusoidally varying overall binocular disparities and ocular vergence movements without perception of motion in depth suggests that these variables are not adequate cues for perception of (change in) depth.

Convergence, Ocular↗
PubMed1995

Time, change, and motion: the effects of stimulus movement on temporal perception.

The effects of stimulus motion on time perception were examined in five experiments. Subjects judged the durations (6-18 sec) of a series of computer-generated visual displays comprised of varying numbers of simple geometrical forms. In Experiment 1, subjects reproduced the duration of displays consisting of stationary or moving (at 20 cm/sec) stimulus figures. In Experiment 2, subjects reproduced the durations of stimuli that were either stationary, moving slowly (at 10 cm/sec), or moving fast (at 30 cm/sec). In Experiment 3, subjects used the production method to generate specified durations for stationary, slow, and fast displays. In Experiments 4 and 5, subjects reproduced the duration of stimuli that moved at speeds ranging from 0 to 45 cm/sec. Each experiment showed that stimulus motion lengthened perceived time. In general, faster speeds lengthened perceived time to a greater degree than slower speeds. Varying the number of stimuli appearing in the displays had only limited effects on time judgments. Other findings indicated that shorter intervals tended to be overestimated and longer intervals underestimated (Vierordt's law), an effect which applied to both stationary and moving stimuli. The results support a change model of perceived time, which maintains that intervals associated with more changes are perceived to be longer than intervals with fewer changes.

Acceleration↗
PubMed1999

Color and luminance in the perception of 1- and 2-dimensional motion.

An isoluminant color grating usually appears to move more slowly than a luminance grating that has the same physical speed. Yet a grating defined by both color and luminance is seen as perceptually unified and moving at a single intermediate speed. In experiments measuring perceived speed and direction, it was found that color- and luminance-based motion signals are combined differently in the perception of 1-D motion than they are in the perception of 2-D motion. Adding color to a moving 1-D luminance pattern, a grating, slows its perceived speed. Adding color to a moving 2-D luminance pattern, a plaid made of orthogonal gratings, leaves its perceived speed unchanged. Analogous results occur for the perception of the direction of 2-D motion. The visual system appears to discount color when analyzing the motion of luminance-bearing 2-D patterns. This strategy has adaptive advantages, making the sensing of object motion more veridical without sacrificing the ability to see motion at isoluminance.

Color Perception↗