Receptive field classes of cells in the striate cortex of the cat

The perceived size of an object depends on its spatial context, in addition to its projected image on the retina and perceived distance. However, how these factors interact with each other to affect perceived object size is still not clear. In this study, we manipulated the binocular disparity of images to assess the effect of perceived distance on perceived object size, as well as background element size to assess the effect of context. The perceived target size under different combinations of perceived distance and context was measured with a two-interval forced-choice paradigm, in which one interval contained a standard disk with a textured background while the other contained a comparison disk on a blank background in each trial. The observers were instructed to indicate which interval contained a larger disk. A staircase procedure was used to measure the point of subjective equality for the perceived target size. Our results showed that the perceived target size increased with the perceived distance while decreased with background element size. In addition, context modulated the relationship between the perceived target size and perceived distance. The data can be explained by a computational model that incorporates several size selective channels whose size sensitivity to a stimulus can be modulated by its disparity. The target response of each channel is subjected to the divisive inhibition signal from the size information in the context. The perceived size is determined by the weighted average of the responses of these size channels. This model can explain more than 91% of variability in the averaged data. Thus, while both perceived distance and context can affect the perceived size of an object, they exert the effect through different mechanisms.

The magnitude of spike-responses of neurons in the mammalian visual system to sine-wave luminance-contrast-modulated drifting gratings is modulated by the temporal frequency of the stimulation. However, there are serious problems with consistency and reliability of the traditionally used methods of assessment of strength of such modulation. Here we propose an intuitive and simple tool for assessment of the strength of modulations in the form of standardized F1 index, zF1. We define zF1 as the ratio of the difference between the F1 (component of amplitude spectrum of the spike-response at temporal frequency of stimulation) and the mean value of spectrum amplitudes to standard deviation along all frequencies in the spectrum. In order to assess the validity of this measure, we have: (1) examined behavior of zF1 using spike-responses to optimized drifting gratings of single neurons recorded from four ‘visual’ structures (area V1 of primary visual cortex, superior colliculus, suprageniculate nucleus and caudate nucleus) in the brain of commonly used visual mammal – domestic cat; (2) compared the behavior of zF1 with that of classical statistics commonly employed in the analysis of steady-state responses; (3) tested the zF1 index on simulated spike-trains generated with threshold-linear model. Our analyses indicate that zF1 is resistant to distortions due to the low spike count in responses and therefore can be particularly useful in the case of recordings from neurons with low firing rates and/or low net mean responses. While most V1 and a half of caudate neurons exhibit high zF1 indices, the majorities of collicular and suprageniculate neurons exhibit low zF1 indices. We conclude that despite the general shortcomings of measuring strength of modulation inherent in the linear system approach, zF1 can serve as a sensitive and easy to interpret tool for detection of modulation and assessment of its strength in responses of visual neurons.

We measured functional input from short-wavelength selective (S) cones to neurons in the dorsal lateral geniculate nucleus (LGN) and striate cortex (area V1) in anaesthetized marmosets. We found that most magnocellular (MC) and parvocellular (PC) cells receive very little (<5%) functional input from S cones, whereas blue-on cells of the koniocellular (KC) pathway receive dominant input from S cones. Cells dominated by S cone input were not encountered in V1, but V1 cells received more S cone input than PC or MC cells. This suggests that S cone inputs are distributed broadly among neurons in V1. No differences in strength of S cone inputs were seen on comparing dichromatic and trichromatic marmosets, suggesting that the addition of a medium-long wavelength selective cone-opponent (“red–green”) channel to a dichromatic visual system does not detectably affect the chromatic properties of the S cone pathways.

This study examines whether neurons in the primary visual cortex (V1) of the cat (also referred to as area 17) are sensitive to boundaries that are delineated by a difference in features other than luminance contrast. Most research on this issue has concentrated on the responses to texture borders (e.g. ‘illusory contours’) and has found neurons that are sensitive to such borders in V2 and to a lesser extent in V1. Here neurons in cat area 17 (V1) were exposed to borders that were oblique to the orientation preference of the neuron and that were created by differences in phase, orientation or direction of motion of two drifting sinewave gratings. Nearby phase borders evoked increased firing in 15 out of 98 neurons, orientation borders in 18 out of 98, and direction borders in 15 out of 70 neurons recorded in area 17 (V1) of anesthetized cats. The firing rates of these neurons were enhanced when a feature border was presented close to their receptive field, partly independent of the cue involved. Control experiments with a contrast border showed that the enhanced firing was due to a release of suppression rather than facilitation. A conceptual model is presented that can describe the data and uncovers a peculiarity of the phase domain compared to the orientation and direction domain. The model unifies the knowledge gained here about orientation-specific center–surround interactions, contextual effects, and end-stopping. The data and model suggest that these phenomena are part of a single mechanism that enables the brain to detect feature discontinuities across a range of features.

The present study investigated the spatial properties of cells in the postero-lateral lateral suprasylvian (PLLS) area of the cat and assessed their sensitivity to edges defined by motion. A total of one hundred and seventeen (117) single units were isolated. First, drifting sinusoidal gratings were used to assess the spatial properties of the cells' receptive fields and to determine their spatial frequency tuning functions. Second, random-dot kinematograms were used to create illusory edges by drifting textured stimuli (i.e. a horizontal bar) against a similarly textured but static background. Almost all the cells recorded in PLLS (96.0%) were binocular, and a substantial majority of receptive fields (79.2%) were end-stopped. Most units (81.0%) had band-pass spatial frequency tuning functions and responded optimally to low spatial frequencies (mean spatial frequency: 0.08 c./degree). The remaining units (19.0%) were low-pass. All the recorded cells responded vigorously to edges defined by motion. The vast majority (96.0%) of cells responded optimally to large texture elements; approximately half the cells (57.3%) also responded to finer texture elements. Moreover, 38.5% of the cells were selective to the width of the bar (i.e., the distance between the leading and the trailing edges). Finally, some (9.0%) cells responded in a transient fashion to leading and to trailing edges. In conclusion, cells in the PLLS area are low spatial frequency analyzers that are sensitive to texture and to the distance between edges defined by motion.

‘Spontaneous’ and visually evoked action potentials were recorded from single neurons in cytoarchitectonic area 17 (striate cortex, area V1) of anaesthetized and immobilized cats, prior to, during and after brief reversible inactivation of the ipsilateral postero-temporal visual (PTV) cortex (presumed homologue of primate inferotemporal cortex). Inactivation of PTV cortex resulted: 1) in significant changes in the response magnitude (mostly a reduction) to optimal and/or sub-optimal visual stimuli in over 55% of area 17 cells and 2) significant changes (usually a reduction) in the ‘spontaneous’ (background) activity of about two-thirds of the cells in which inactivation of PTV cortex significantly affected the magnitude of responses to optimal stimuli. In over 85% of the significantly affected area 17 cells, rewarming PTV cortex to normal temperature (36 °C) resulted in the recovery of both the magnitude of responses and the background activity to levels not significantly different from pre-inactivation levels. Irrespective of the significance of changes in the magnitude of responses, in a substantial proportion of area 17 cells, inactivation of PTV cortex resulted in changes in some receptive field characteristics. Thus, there were substantial (20% or more) changes in orientation tuning widths (in over a quarter of the sample) and/or direction selectivity indices (in about a third of the sample). Thus, the feedback signals originating from PTV cortex, like signals originating from some other ‘higher-order’ visual cortical areas exert a clear modulatory influence on the responsiveness, background activity and some receptive field properties of neurons in the ipsilateral area 17.