PubMed Health⌕ Search

Biomedical subjects

D H Grosof

Publications and source records attributed to D H Grosof.

6 recordsLinked to original sources
PubMed1992

Higher-order factors influencing the perception of sliding and coherence of a plaid.

The effect of several new stimulus parameters on the perception of a moving plaid pattern (the sum of two sine-wave gratings) were tested. It was found that: (i) the degree of perceived sliding is strongly influenced by the aperture configuration through which the plaid is viewed; (ii) the chromaticity of the sinusoidal components affects coherence in that more sliding is observed when the plaid components differ in hue, and there is less sliding when they are of the same hue; (iii) equiluminant plaids made of components equal in color almost never show any sliding; and (iv) sliding increases with viewing time. The coherence-sliding percept must therefore be influenced by color, by global interactions, and by adaptation or learning effects, thus suggesting a higher-level influence. These results are most easily modelled by separating the decision to carry out recombination from the process of recombination.

Attention↗
PubMed1992

Properties of the recombination of one-dimensional motion signals into a pattern motion signal.

We have examined the human ability to determine the direction of movement of a variety of plaid patterns. The plaids were composed of two orthogonal sine-wave gratings. When the plaid components are of unequal spatial frequency or sometimes of unequal contrast, observers judge the direction of movement incorrectly. In terms of the two-stage model of Adelson and Movshon (1982), these errors may result from either a misjudgment in the perceived speeds of each of the components or a failure in the combination of one-dimensional component movements into a coherent direction of motion of the two-dimensional plaid pattern, or both. A comparison of the perceived direction of motion of plaids with the relative perceived speeds of the plaid component gratings suggest that both failures occur, but in different circumstances. The relative perceived speed of the plaid components was measured with a spatial and a temporal forced-choice technique, the former leading to larger differences. Our results support the notion that the visual system decomposes a moving plaid into oriented components and subsequently recombines the component motions.

Adult↗
PubMed1991

Classifying simple and complex cells on the basis of response modulation.

Hubel and Wiesel (1962; Journal of Physiology, London, 160, 106-154) introduced the classification of cortical neurons as simple and complex on the basis of four tests of their receptive field structure. These tests are partly subjective and no one of them unequivocally places neurons into distinct classes. A simple, objective classification criterion based on the form of the response to drifting sinusoidal gratings has been used by several laboratories, although it has been criticized by others. We review published and unpublished evidence which indicates that this simple and objective criterion reliability divides neurons of the striate cortex in both cats and monkeys into two groups that correspond closely to the classically-described simple and complex classes.

Animals↗
PubMed1989

Spatial-frequency organization in primate striate cortex.

We measured the spatial-frequency tuning of cells at regular intervals along tangential probes through the monkey striate cortex and correlated the recording sites with the cortical cytochrome oxidase (CytOx) patterns to address three questions with regard to the cortical spatial-frequency organization. (i) Is there a periodic anatomical arrangement of cells tuned to different spatial-frequency ranges? We found there is, because the spatial-frequency tuning of cells along tangential probes changed systematically, varying from a low frequency to a middle range to high frequencies and back again repeatedly over distances of about 0.6-0.7 mm. (ii) Are there just two populations of cells, low-frequency and high-frequency units, at a given eccentricity (perhaps corresponding to the magno- and parvocellular geniculate pathways) or is there a continuum of spatial-frequency peaks? We found a continuum of peak tuning. Most cells are tuned to intermediate spatial frequencies and form a unimodal rather than a bimodal distribution of cell peaks. Furthermore, the cells with different peak frequencies were found to be continuously and smoothly distributed across a module. (iii) What is the relation between the physiological spatial-frequency organization and the regions of high CytOx concentration ("blobs")? We found a systematic correlation between the topographical variation in spatial-frequency tuning and the modular CytOx pattern, which also varied continuously in density. Low-frequency cells are at the center of the blobs, and cells tuned to increasingly higher spatial frequencies are at increasing radial distances.

Animals↗
PubMed1988

Responses of simple and complex cells to random dot patterns: a quantitative comparison.

1. There are several reports that random dot patterns are potent stimuli for cortical complex cells but not for simple cells. This finding is regarded as evidence against Hubel and Wiesel's hierarchical model of cortical circuitry, in which simple cells are the principal input to complex cells. We have reinvestigated the question quantitatively by recording responses to dot patterns from 106 cells in area 17 and the 17/18 border region of normal adult cats. 2. The cells were classified as simple (n = 62) or complex (n = 40) (4 were end stopped or hypercomplex) on the basis of whether they gave modulated (AC) or unmodulated (DC) responses to drifting sine gratings. 3. Although there are large within-group differences, we found both simple and complex cells that respond to bright random dots on a dark background, drifted across the receptive field at 3 degrees/s. The responses at the optimal direction averaged 6.2 and 18.1 spikes/s (spontaneous activity subtracted) for simple and complex cells, respectively. 4. We also recorded responses to drifting sine gratings. Complex cells were also found to respond more than simple cells to these stimuli. For each cell, we calculated a dot index expressing the dot response relative to grating response. The dot index averaged 0.43 for simple cells and 0.55 for complex cells. It therefore appears that much of the difference in response to dot patterns reflects a difference in general responsivity. 5. In subsamples of cells, we examined the effects of varying dot density, dot size, and drift velocity. These variables affect different cells in a manner largely independent of cell class. Most simple cells in our sample responded well to random dot patterns at several velocities, at two different dot sizes and at both 3 and 50% dot densities. 6. Our results agree with previous studies in showing that complex cells respond more vigorously than simple cells to dot patterns, but the fact that many simple cells also respond to these stimuli makes our results consistent with a hierarchical model of cortical circuitry.

Animals↗