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S Hochstein

Publications and source records attributed to S Hochstein.

At least 19 recordsLinked to original sources
PubMed1992

Asymmetric interactions in the processing of the visual dimensions of position, width, and contrast of bar stimuli.

The processing of different dimensions of a single stimulus may be either integral or separable. Dimensions are called integral if correlated variation of one improves discrimination on the basis of the other and random variation of one interferes with discrimination on the basis of the other. For separable dimensions on the other hand, subjects can attend to one dimension and disregard variations in the other. These discrimination tests were used to find the interactions between the processing of the visual dimensions of position, width, and contrast of a light bar stimulus. The relations between these dimensions were found to be asymmetric: judgments of position and width are independent of contrast variations, but variations in these dimensions influence contrast discriminations. Furthermore, position variations influence width judgements more than vice versa. The data were analyzed for repetition effects, and it was found that this model is not sufficient to explain all the interaction phenomena. The asymmetries found may be related to the different ways these dimensions are mapped onto cortical neuron responses.

Contrast Sensitivity↗
PubMed1992

Characteristics of the flux dimension cue in apparent motion correspondence.

It has been shown that element flux and size (but not luminance) serve as correspondence cues in the apparent motion visual system. Results are now presented of a study of the characteristics of the flux cue. It was found that flux rather than luminance is used by the system even when the size of the elements is greater than the size limit of Ricco's law. There were interactions between the apparent motion processing of the size and flux dimensions, beyond the obvious dependence of flux on size: positively correlated size and flux differences between elements have a greater effect on correspondence than do negatively correlated differences. Finally, when comparing the fluxes of different elements, the apparent motion system uses relative flux (above or below background) rather than absolute flux (relative to zero).

Humans↗
PubMed1991

Gender differences in apparent motion perception.

Distance disparity is a strong cue to element correspondence in apparent motion. Using a 2-AFC paradigm we have previously shown that shape similarity also plays a role. We now demonstrate a small gender difference in these effects: women are more sensitive to distance disparity, whereas men are more sensitive to differences in shape. Furthermore, in the competing presence of a shape cue, women's sensitivity to distance decreases while men's sensitivity is unaffected. These observations may be related to putative gender differences in the 'form' and 'motion-spatial relations' cortical pathways.

Adult↗
PubMed1990

Time course of perceptual discrimination and single neuron reliability.

The reliability of identification of a visual target increases with time available for inspection of the stimulus. We suggest that the neural basis of this improvement is the existence of a mechanism for integrating a noisy firing rate over some period, leading to a reduction in mean firing rate variance with available processing time. We have determined the experimental time course of the improvement in reliability in a parallel search task where the available inspection time is limited by the presentation of a mask at various times after a brief stimulus. We compare the resulting psychometric functions with the predictions of a model based on Signal Detection Theory. The model is based on the assumption that the reliability of the observer's response is limited by the variability of the responses of individual neurons. The reliability of the discrimination between two stimuli at the neuronal level is then directly related to the ratio of the difference between their integrated mean responses (over many trials) to the response standard deviation. This reliability increases with inspection time. To demonstrate application of the model to electrophysiological data, "neurometric functions" are derived from the firing rates of a monkey V1 cortical neuron. The data were obtained while the animal was active in a discrimination task. The results correspond qualitatively to our observed human psychometric functions.

Animals↗
PubMed1990

On and off pathway contributions to apparent motion perception.

We studied the separability and/or interaction of the On and Off pathways in their role as inputs to visual motion perception. Using the long-range motion perception system, we asked if the motion system can use brightness polarity information, by testing whether correspondence is preferred between elements for which brightness polarity is preserved. We found such a preference, suggesting that brightness polarity information is indeed available to the motion system. However, under certain conditions motion is perceived even though the brightness polarity of apparent motion stimulus elements is reversed, indicating that the apparent motion system does integrate information from these two pathways. The source of the preference for maintaining polarity seems not to be the different brightnesses of the dark and bright stimulus elements, but the very fact that information must be integrated from different pathways. We relate the characteristics of the dependence of the motion perception on element contrast and contrast sign to those of previously reported visual evoked potential responses to brightness increments and decrements.

Contrast Sensitivity↗
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↗
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↗