Biomedical subjects

J P Gaska

Publications and source records attributed to J P Gaska.

7 recordsLinked to original sources

PubMed1992

Interneuronal interaction between members of quadrature phase and anti-phase pairs in the cat's visual cortex.

Interactions between adjacent simple cells recorded simultaneously from the same microelectrode placement were studied by correlational analysis. The receptive fields of pairs of such cells exhibit either 90 degrees (quadrature phase) or 180 degrees (anti-phase) phase relationships. We now show that the majority of quadrature phase pair members do not receive common input from the immediately precedent stage along the visual pathway, nor do these cells interact with each other. The anti-phase pairs show relatively strong mutual inhibition. These results suggest that each of the physically adjacent phase-related simple cells receives excitatory input from a distinct group of pre-cortical cells, and that mutual inhibitions between members of anti-phase pairs are used to construct the inhibitory subzones of these cells. We propose a model which incorporates these new results and provides a parsimonious explanation for the construction of both quadrature phase and anti-phase pairs.

Animals↗

PubMed1990

Structural classification of multi-input nonlinear systems.

We present new structural classification and parameter estimation results that are applicable to multi-input nonlinear systems. The mathematical relationships between the self- and cross-(Volterra and Wiener) kernels are derived for a basic two-input nonlinear structure. These results are then used to develop classification methods for more complicated two-input structures. Algorithms for estimating the parameters (linear and nonlinear subsystems) of these structures are also presented.

Cybernetics↗

PubMed1988

Spatial and temporal frequency selectivity of neurons in visual cortical area V3A of the macaque monkey.

Response properties of neurons in V3A were studied at a retinal eccentricity of 2-4 deg. The distributions of spatial frequency bandwidths and orientation bandwidths were similar to those of neurons in V1. Peaks of spatial frequency tuning curves ranged from 0.35 to 8.0 c/deg with a mean of 1.75 c/deg. Most V3A cells showed lowpass or, less often, broad bandpass temporal frequency selectivity. The mean direction selectivity index was 0.41. The response properties of cells in V3A differed most from those in V1 with respect to the larger receptive field widths in V3A averaging about 4 deg, the consequent larger number of cycles of the preferred grating that fall within the receptive field, and the previously reported profound response suppression incurred when patches of the preferred grating are extended both within and beyond the classical receptive field. The response properties of cells in V3A differed most from those in V3 in that V3A neurons are much less selective to the speed and direction of stimulus motion than are neurons in V3. The overall response properties of cells in V3A are consistent with anatomical evidence that places this cortical area in the visual pathway from V3A to V4 and then to IT.

Animals↗

PubMed1988

Responses of simple and complex cells to compound sine-wave gratings.

We have studied the responses of simple and complex cells in the primary visual cortex of the cat to rigidly drifting compound sine-wave gratings as a function of the phase offset between fundamental and harmonic frequencies that both fell within the passband of the cell. Simple cells show phase-dependent increases and decreases in peak and mean response which are predictable on the basis of a cell's line weighting function. However, the amplitudes and phases of the base and harmonic frequencies in the response are, in general, not well predicted by the relationships of these same components in the compound grating stimuli. These distortions are shown to be largely a consequence of the rectification that follows linear summation at the simple cell stage. Such distortions are, in principle, correctable when the responses of a second simple cell, as part of a 180 deg phase pair, are taken into account. Complex cells typically showed a strong nonlinear response component at the difference frequency of drifting compound gratings. This was sometimes accompanied by a linear response component at one, or both, of the separate stimulus frequencies. Information about the absolute phases of the frequency components of a compound grating is not preserved in the nonlinear response of complex cells; however, information about the local phase difference between the gratings is preserved. In effect, the nonlinear component of the complex cell response is proportional to the time-varying signal envelope that results from the mutual interference of stimulus frequencies that fall in the cell's spatial receptive field and frequency passband.

Animals↗

PubMed1987

Diversity of complex cell responses to even- and odd-symmetric luminance profiles in the visual cortex of the cat.

We have tested the hypothesis that complex cell receptive fields are made up of subfields which, for a given cell, have either exclusively even or exclusively odd symmetry. To do this we have measured the response of complex cells in the visual cortex of the cat to members of pairs of spatially limited even-symmetric stimuli (single light and dark bars) and pairs of odd-symmetric stimuli ("light-dark" and "dark-light" double bars) successively drifting across their receptive fields. The strength of a cell's response was estimated by measuring the sum of all spikes produced by a stimulus. Some complex cells respond about equally to single light and dark bars; others respond appreciably more to either the light or dark bar. The central tendency of average response histograms was estimated by measuring the mean with respect to position across the width of the receptive field. Many complex cells show distinct spatial offsets between the mean for narrow single light and that for dark bars as well as between means to double bars of opposite phase. Combined offset plots were constructed with the spatial offsets between means for single light bars and single dark bars along the x axis and the offsets between means to double bars of opposite phase along the y axis. There is significant scatter in the combined offset points; some falling at the origin, some at significant distances from the origin along the axes, and others well within each of the four quadrants. These diverse localizations in the offset plots rule out the simple models of complex cell spatial substructure described above and, therefore, imply considerable heterogeneity within the population of complex cells.

Animals↗

PubMed1987

Response suppression by extending sine-wave gratings within the receptive fields of neurons in visual cortical area V3A of the macaque monkey.

Even though there are many more cycles of the "optimal" grating extending across the receptive fields of cells in V3A than of cells in V1 and V2, the spatial frequency bandwidths in V3A are no narrower than in V1 or V2. Thus, the inputs to V3A cells are not combined in a phase coherent manner across the entire receptive field. Moreover, the defined receptive fields of cells in V3A are generally surrounded by suppressive regions which are, on average, much stronger than those found for neurons in V1 and V2. Even within the classical receptive field, most neurons in V3A respond far more vigorously to a limited patch of a few cycles of a grating at the preferred spatial frequency than to wider grating stimuli. This intra-receptive field suppression demonstrates a new level of response complexity, and suggests that V3A cells may antagonistically combine nonlinear mechanisms that themselves encode stimulus energy over a restricted region of space and spatial-frequency.

Animals↗

PubMed1985

Spatial and temporal frequency selectivity of neurones in visual cortical areas V1 and V2 of the macaque monkey.

The spatial and temporal frequency selectivity of 148 neurones in the striate cortex, V1, and of 122 neurones in the second visual cortical area, V2, of the macaque monkey were studied using sine-wave gratings of suprathreshold contrast drifting over the receptive field at the preferred orientation and direction. Neurones in V1 and V2 were selective for different but partially overlapping ranges of the spatial frequency spectrum. At retinal eccentricities of 2-5 deg from the fovea, the spatial frequency preferences for neurones ranged from 0.5 to 8.0 cycles/deg in V1 and from 0.2 to 2.1 cycles/deg in V2 and were on average almost 2 octaves lower in V2 than in V1. Spatial frequency full band widths in the two cortical areas were in the range 0.8-3.0 octaves, with a mean value of 1.8 octaves, in the parafoveal representation of both V1 and V2, and 1.4 and 1.6 octaves respectively in the foveal representation of V1 and V2. Most neurones in V1 and some in V2 responded well at temporal frequencies up to 5.6-8.0 Hz before their responses dropped off at still higher frequencies. In V1, 68% of the neurones exhibited low-pass temporal tuning characteristics and 32% were very broadly tuned, with a mean temporal frequency full band width of 2.9 octaves. However, in V2 only 30% of the neurones showed low-pass temporal selectivity and 70% of the cells had bandpass temporal characteristics, with a mean full band width of 2.1 octaves. In V2 the minimal overlap of bandpass tuning curves across the temporal frequency spectrum suggests that there are at least two distinct bandpass temporal frequency mechanisms as well as neurones with low-pass temporal frequency tuning at each spatial frequency. A matrix of spatial and temporal frequency combinations was employed as stimuli for neurones with bandpass temporal frequency selectivity in both V1 and V2. The resultant spatio-temporal surfaces provided evidence that a neurone's preference for spatial frequency is essentially independent of the test temporal frequency; however, in V2 there was some tendency for temporal frequency peaks to shift slightly towards lower frequencies when non-optimum values of spatial frequency either above or below the preferred value were tested. Neurones with pronounced directional selectivity were encountered over a wide range of spatial frequencies, although in both cortical areas there was a tendency for an increased incidence of directional selectivity among neurones which were selective for lower spatial frequencies and higher temporal frequencies.

Animals↗