Biomedical subjects

S S Shimozaki

Publications and source records attributed to S S Shimozaki.

5 recordsLinked to original sources

PubMed2001

Effects of luminance oscillations on simulated lightness discriminations.

The speed of processes underlying lightness constancy was studied by having observers discriminate small differences in simulated lightness under an oscillating illumination. The period of oscillation varied from 0.25 to 120 sec. The target was a 1 degrees square which appeared for 150 msec at random intervals either directly against a uniform background or separated from the background by a 1 degrees dark gap. When the target and background were adjacent to each other, discrimination accuracy approached control levels (fixed illumination) at all but the shortest periods of oscillation. When the gap was introduced, accuracy increased as the period of oscillation increased, but never approached control levels. The results suggest that a fast local contrast mechanism is the primary mediator of lightness constancy for this task, but that there is also a slower mechanism that may be related to adaptation.

Adult↗

PubMed2000

A signal detection model predicts the effects of set size on visual search accuracy for feature, conjunction, triple conjunction, and disjunction displays.

Recently, quantitative models based on signal detection theory have been successfully applied to the prediction of human accuracy in visual search for a target that differs from distractors along a single attribute (feature search). The present paper extends these models for visual search accuracy to multidimensional search displays in which the target differs from the distractors along more than one feature dimension (conjunction, disjunction, and triple conjunction displays). The model assumes that each element in the display elicits a noisy representation for each of the relevant feature dimensions. The observer combines the representations across feature dimensions to obtain a single decision variable, and the stimulus with the maximum value determines the response. The model accurately predicts human experimental data on visual search accuracy in conjunctions and disjunctions of contrast and orientation. The model accounts for performance degradation without resorting to a limited-capacity spatially localized and temporally serial mechanism by which to bind information across feature dimensions.

Adult↗

PubMed1999

The maintenance of apparent luminance of an object.

Results from luminance discriminations with objects defined by apparent motion suggest an object-specific temporal integration of luminance. Further experiments suggested that this integration is weighted to favor the initial display of an object and involves the percept of surface reflectance (lightness). These results are consistent with the object-file metaphor suggested by D. Kahneman, A. Treisman, and B. Gibbs (1992), in which an object's perceived initial surface reflectance is assigned and maintained in an object file. A strategy is proposed in which the intrinsic properties of an object are assumed not to change over time. As intrinsic properties are generally invariant and possibly difficult to compute, this strategy would have the advantage of relatively high accuracy at relatively low computational cost.

Adult↗

PubMed1993

The role of Fourier components in discrimination between two types of plaid patterns.

Do decision processes have separate access to the individual Fourier components of a complex pattern? Subjects discriminated between plaid patterns formed by multiplying or by summing vertical and horizontal square-wave gratings. Such patterns differ in two ways: (1) product plaids contain distinctive off-axis Fourier components; (2) adjacent luminances are related by equal ratios in the products and by equal differences in the sums. Performance on this task was compared with the separately measured unmasked detection thresholds of the off-axis Fourier components and with performance in control tasks which provided only the non-Fourier cues. Performance in the plaid discrimination was worse than predicted from the unmasked detection thresholds, but better than predicted from the control tasks. The results argue that Fourier components are accessible, but that masking reduces their usefulness.

Discrimination, Psychological↗

PubMed1992

Using distinctive Fourier components to discriminate between complex patterns.

Observers discriminated between a plaid pattern formed by summing vertical and horizontal cosine gratings, and a plaid formed by multiplying the gratings. Such patterns are alike with respect to many non-Fourier primitives, but differ in the Fourier domain by diagonal components which are present in the plaid formed by multiplication, but not in the one formed by summing. When discrimination performance is related to the contrast of the diagonal components, it is found that the contrast threshold for discrimination is approximately the same as the threshold for detection of the isolated components. However, the psychometric function for discrimination is shallower than that for detection, suggesting the presence of masking. Despite the masking, the results support the proposition that discrimination processes may operate directly on the representations of local Fourier components.

Contrast Sensitivity↗