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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↗
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↗
PubMed1976

Linear and nonlinear spatial subunits in Y cat retinal ganglion cells.

1. The mechanism which makes Y cells different from X cells was investigated. 2. Spatial frequency contrast sensitivity functions for the fundamental and second harmonic responses of Y cells to alternating phase gratings were determined. 3. The fundamental spatial frequency response was predicted by the Fourier transform of the sensitivity profile of the Y cell. The high spatial frequency cut-off of a Y cell's fundamental response was in this way related to the centre of the cell's receptive field. 4. The second harmonic response of a Y cell did not cut off at such a low spatial frequency as the fundamental response. This result indicated that the source of the second harmonic was a spatial subunit of the receptive field smaller in spatial extent than the centre. 5. Contrast sensitivity vs. spatial phase for a Y cell was measured under three conditions: a full grating, a grating seen through a centrally located window, a grating partially obscured by a visual shutter. The 2nd/1st harmonic sensitivity ratio went down with the window and up with the shutter. These results implied that the centre of Y cells was linear and also that the nonlinear subunits extended into the receptive field surround. 6. Spatial localization of the nonlinear subunits was determined by means of a spatial dipole stimulus. The nonlinear subunits overlapped the centre and surround of the receptive field and extended beyond both. 7. The nature of the Y cell nonlinearity was found to be rectification, as determined from measurements of the second harmonic response as a function of contrast. 8. Spatial models for the Y cell receptive field are proposed.

Action Potentials↗
PubMed1976

Theoretical analysis of parameters leading to frequency modulation along an inhomogeneous axon.

1. Theoretical computations were conducted on a computer model of a segmented, nonhomogeneous axon to understand the mechanism of frequency block of conduction. 2. The model is based on the Hodgkin-Huxley equations modified in several ways to better describe the cockroach axon. We used cockroach parameters where available. 3. The increase in fiber radius was spread over a series of segments to approximate a taper. We found that a taper allows a larger overall increase in fiber diameter than a single step to be successfully passed. 4. We studied effects on a train of impulses. The modified equations included effects due to changes in extracellular potassium concentration resulting from the repetitive firing of the axon. 5. An increase in diameter which allows a single spike to pass blocks the subsequent impulses in a train at the taper if potassium concentration variability is introduced. This could explain the low-pass filter characteristics of axon constrictions. 6. Results of the model fit well with the experiemental spike shape and height. Data were computed for the refractory period and its dependence on the taper parameters.

Action Potentials↗