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S Hochstein

Publications and source records attributed to S Hochstein.

At least 37 records · Page 2Linked to original sources
PubMed1989

Size, flux and luminance effects in the apparent motion correspondence process.

The effects of the relative size, luminance, and total luminous flux of apparent motion visual stimulus disk elements are studied, using a competitive paradigm. These dimensions can only be studied in pairs and we find that all three pairs have significant correspondence process effects. A comparison of the magnitudes of the effects, however, suggests that size and flux are the dimensions relevant to apparent motion processing, while luminance may not contribute to the correspondence process. Pitting distance against these dimensions in apparent motion tasks, we were able to find effective equivalence scales among them. Finally, interactions were found between the processing of some of these dimensions. The most pronounced interaction effect is that the addition of the size dimension increases the noise in the processing of distance, while size processing is not affected by the addition of the distance cue.

Humans↗
PubMed1989

How serial is serial processing in vision?

Visual search for an element defined by the conjunction of its colour and orientation has previously been shown to be a serial processing task since reaction times increase linearly with the number of distractor elements used in the display. Evidence is presented that there are parallel processing constituents to this serial search. Processing time depended on the ratio of the number of the two distractor types used, suggesting that only one type was scanned. Which type was scanned also depended on the distractor ratio, indicating that this decision was made after stimulus presentation and was based on a parallel figure-ground separation of the stimulus elements. Furthermore, in accordance with this serial scanning model, there was an increase in processing speed (elements scanned per second) with increase in number of elements to be scanned. This increased efficiency suggests that clumps of elements were processed synchronously. Under the stimulation conditions used, clumps contained six to sixteen elements and each clump was processed in 50-150 ms.

Attention↗
PubMed1989

Visual orientation estimation.

A systematic error is reported in orientation estimation, in that on average, estimates are closer to the vertical axis than are the stimuli by up to 6 degrees. This systematic error results from a specific mechanism that may be related to depth perception, and that is avoided in certain circumstances or when other mechanisms take over. For example, the estimates of one observer who was a well-trained professional draughtsman did not show this systematic error. Furthermore, for all observers tested, estimation of clock time is not subject to the regular orientation estimation error. Rather, observers tend to estimate times as slightly further from the quarter hour than they really are. Orientation judgement channel capacity was also studied under various conditions. The number of discriminable orientations is far above the magic number "7" limit, reaching over 20 in optimal circumstances. The distribution of discriminable orientations is nonlinear, in that these are more closely packed about the horizontal and vertical axis than at the oblique.

Attention↗
PubMed1988

Shape similarity and distance disparity as apparent motion correspondence cues.

Apparent motion is perceived when two spots of light are presented successively in different locations. When more than one element is present in each frame, there is a correspondence problem in matching the elements in one frame with those in the other. We report the effects of shape similarity and distance disparity on the correspondence process. Twenty subjects were tested using a 2-AFC design. We found that both shape and distance cues are used by the correspondence process: when distance is the only cue the motion which is usually perceived is that involving the shorter distance; when shape is the only cue the motion involving two elements of the same shape is preferred. We also studied the interaction between the two cues when both were present. Quantitative measures of the relative strengths of these effects and of their interaction are reported. A Signal Detection Theory model is used to analyze these apparent motion correspondence effects.

Cues↗
PubMed1988

Interactions in the discrimination and absolute judgement of orientation and length.

An asymmetric model is described for interactions in the perception of two dimensions (length and orientation) of a single visual stimulus. Two methods were used to test these interactions, and models for the interpretation of the possible outcomes of these tests are discussed. A length discrimination task showed facilitation (decreased reaction time) when orientation was covaried with length, and interference (increased reaction time) when random orientation variation was introduced. A smaller effect was seen when length was varied in an orientation discrimination task in a correlated or random fashion. Analysis of sequential effects showed that reaction times are fastest on repetition trials and are slowed by either the need to change the response or the need for additional sensory processing. With the second method, it was found that the amount of information transmitted in the estimation of orientation was not affected by the introduction of the redundant dimension of length, but that there was a significant gain in the amount of information transmitted in the estimation of length by the addition of the redundant dimension of orientation. It is concluded that orientation is probably a perceptual primitive of the visual system whereas length is a computed variable.

Adult↗
PubMed1985

Simple- and complex-cell response dependences on stimulation parameters.

We studied the response time course and amplitude dependence on stimulation parameters in cat cortical visual neurons to determine their receptive-field spatial-summation characteristics. Response poststimulus time (PST) histograms of cortical simple cells to contrast-reversal grating stimulation generally have a single peak for each stimulus temporal cycle, though the responses appear rectified. In response to contrast-reversal grating stimulation the general PST histogram time course for complex cells is two peaks, though often these peaks are of different amplitudes. The time course of complex-cell responses, and the ratio of these two response peaks often varies with stimulation parameters. The appearance of a single response peak in simple cells is reflected in the dominance of the odd harmonic Fourier portion, whereas the half-wave rectification leads to a considerable even harmonic portion. Still, this even portion is never significantly greater than the odd portion. When complex cell PST histograms have two nearly equal peaks, Fourier transformation reveals almost only even harmonic components. When the histogram contains two peaks of unequal amplitude Fourier analysis reveals large odd and even components. An even:odd Fourier harmonic portion ratio larger than 1 may be seen as a defining characteristic of complex cells, differentiating them from simple cells. Histograms with two unequal peaks appear "mixed," containing something of the "pure" single-peaked response and something of the pure double-peaked response. The degree to which the response is mixed may be measured by the ratio of the even:odd portion amplitudes. There is a great degree of variability with stimulation parameters (both spatial phase and spatial frequency) of the time course of mixed responses as opposed to the case of responses that have two equal peaks independent of stimulation grating phase and frequency. In both simple and complex cells there is a close coincidence of the spatial frequency ranges over which the even and odd portions are substantial, though many complex cells show a periodic variation of the even:odd portions ratio. This spatial-frequency dependence differs from that of LGN Y-cells where the odd portion dominates at low spatial frequencies and the even portion at high spatial frequencies. The ratio of even-to-odd portion cut-off is close to 3:1 in all Y-cells, a characteristic we did not find in cortical simple or complex cells. We suggest, therefore, that the nonlinearity of these complex cells does not derive from that of Y-cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

A complex-cell receptive-field model.

The time course of the response of a single cortical neuron to counterphase-grating stimulation may vary as a function of stimulation parameters, as shown in the preceding paper (19). The poststimulus-time histograms of the response amplitudes against time are single or double peaked, and where double peaked, the two peaks are of equal or unequal amplitudes. Furthermore, the spatial-phase dependence of cortical complex-cell responses may be a function of spatial frequency, so that the receptive field appears to have linear spatial summation at some spatial frequencies and nonlinear spatial summation at others (19). In the first part of this paper, we analyze a model receptive field that displays this behavior, and in the second part experimental data are presented and analyzed with regard to the model. The model cortical receptive field in its simplest form contains (two rows) of geniculate X-cell-like, DOG (difference-of-Gaussians)-shaped, center-surround antagonistic, circular-input subunits. We propose nonlinear summation between these two subunits, by introducing a half-wave rectification stage before pooling. The model is tested for the responses it predicts for the application of counterphase-grating stimulation. This simple model predicts the appearance of three response forms as a function of counterphase-stimulation parameters. At periodic spatial frequencies the expected-response histogram has a single peak, whose amplitude has a sinusoidal dependence on spatial phase. At spatial frequencies halfway between these, the expected-response histogram has two equal peaks whose amplitudes have a full-wave rectified sinusoidal dependence on spatial phase. At all intermediate spatial frequencies the expected-response histogram has a "mixed" form; the histogram appears sometimes with one peak, sometimes with two equal peaks, and generally with two peaks of unequal amplitude, as a function of spatial phase. Null responses are expected to appear at specific spatial phases only for the periodic spatial frequencies that give "pure" response time courses as in paragraph 5 above, and not in the more common mixed response case of paragraph 6. The analysis procedure described in the preceding paper (19) is used, separating the odd and even Fourier components of the response histograms reflecting the receptive-field intrasubunit linear summation and intersubunit nonlinear summation, respectively. We propose that this model may be used as a working hypothesis for the analysis of these aspects of the various cortical receptive-field types. Experimental data are described and discussed in terms of the model.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

Zero-crossing detectors in primary visual cortex?

David Marr and others have hypothesized that the visual system processes complex scene information in stages, the first of which involves the detection of light intensity edges or "zero-crossings" (Marr, 1982). Ideal zero-crossing detector mechanisms have been described and modeled in terms of their possible physiological implementation (Marr and Hildreth, 1980; Poggio, 1983). We now present evidence of visual cortical receptive fields which resemble in spatial organizational terms the requirements of zero-crossing analysis. The linear and nonlinear summation within and between the receptive field subunits are described and compared with predicted processes. The relative subunit sizes and separations are analyzed in these terms. Our findings support the notion that receptive fields may correspond with zero-crossing filters rather than zero-crossing detector gates.

Animals↗
PubMed1984

The contrast dependence of spatial frequency channel interactions.

Interactions between spatial frequency channels were tested in two ways: we measured the discriminability by the visual system between two compound spatial-frequency gratings, of components with spatial frequencies in the ratio 1:3, when the difference between the two gratings was an increase (or decrease) in contrast of both components of the compound grating (contrast discrimination), or when the difference between the two gratings was an increase in contrast of one component and a decrease in contrast of the other component (pattern discrimination). We found that the contrast: pattern discriminability ratio differs significantly from unity in most conditions. Furthermore, this ratio is generally greater when the components of the grating are in peaks-add relative phase than when in peaks-subtract phase. On the other hand, the ratio was close to unity for grating components of spatial frequencies 1 and 9 cycles/deg. These results suggest that the human visual system contains spatial frequency channels with bandwidths of between 1.6 and 3.2 octaves and that these relatively broad channels have peaks-add spatial profiles. The channels appear linear at intermediate contrasts and spatial frequencies, but super-linear at high spatial frequencies and contrasts. Contrast and spatial frequency may be interchangeable for the determination of the linearity of the visual system.

Discrimination, Psychological↗
PubMed1983

Discriminability of suprathreshold compound spatial frequency gratings.

We have investigated the detectability of small contrast changes in compound suprathreshold gratings, containing two sinusoidal components. We examined the relationship between the detectability of changes in each of the components alone and the detectability of changes in the two components together. It was found that for the pairs of spatial frequencies 1 and 9 c/deg there is a square law summation, but for spatial frequency pairs omega and 3 omega there is a greater summation which depends on the relative phases of the gratings' components. The results indicate the existence of broadband phase selective spatial frequency channels, of 2 octaves bandwidth.

Discrimination, Psychological↗
PubMed1976

Nonlocal interactions in the photoreceptor transduction process.

We have recently demonstated the dissection of the transduction process in the barnacle photoreceptor into antagonistic "excitor" and "inhibitor" processes. We now show that (a) the interaction between the two processes proceeds even when they are induced in different pigment molecules; (b) the excitor process appears to be slightly facilitated if those pigment molecular unaffected by the stimulus are in the stable metarhodopsin state or slightly inhibited if they are in the rhodopsin state; (c) there is a facilitatory interaction among the excitor processes induced in different pigment molecules. In case a, the interaction has a range of at least a few hundred angstroms, taking place in a time of less than a fraction of a second; in cases b and c, the range could be as little as "nearest neighbors" and the time as much as a few seconds. All these interactions could be intermediated by the "excitor" if it is a transmitter.

Animals↗
PubMed1976

Quantitative analysis of retinal ganglion cell classifications.

The classification of cat retinal ganglion cells as X or Y on the basis of linearity or nonlinearity of spatial summation has been confirmed and extended. Recordings were taken from optic tract fibres of anaesthetized, paralysed cats. 2. When an alternating phase sine wave grating was used as a stimulus, X cells had null positions and Y cells responded at all positions of the grating. 3. These results did not depend on the temporal wave form or the temporal frequency of pattern alternation over a wide range. 4. At high spatial frequencies for the particular cell, a Y cell gave abig 'on-off' response, or frequency doubling, at all positions of the grating, while an X cell did not. 5. The use of contrast sensitivity versus spatial phase also served to differentiate the two cell types. With an alternating sine grating stimulus X cells had a sinusoidal dependence on spatial phase, while each Y cell's sensitivity depended in a complicated manner on spatial phase. 6. Sensitivity versus spatial phase for different Fourier components of the neural response also separated the two classes of cells. Significant second harmonic distortion was present in Y cells. The second harmonic component was spatial phase insensitive, and became dominant at high spatial frequencies. 7. The maximum of the 2nd/1st harmonic ratio was taken as an index of nonlinearity. X cells always had a nonlinearity index less than 1 while in Y cells this index always exceeded 1. 8. Response to spots, diffuse light and drifting gratings were compared to the nonlinearity index as a basis for classifying cells. The nonlinearity index was most reliable because it was least dependent on retinal eccentricity.

Action Potentials↗