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L A Olzak

Publications and source records attributed to L A Olzak.

10 recordsLinked to original sources
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

Configural effects constrain Fourier models of pattern discrimination.

Many models of spatial pattern discrimination assume that judgments are based on information directly available from mechanisms tuned to limited ranges of spatial frequency and orientation. We tested the validity of this assumption for spatial frequency, orientation, and contrast information in a series of complex pattern discrimination experiments. Observers discriminated between simple gratings, between gratings masked by components that differed widely in spatial frequency and/or orientation, and between patterns that presented two cues to discrimination, one in each frequency and/or orientation band. Component cues were combined either in rigid-object correspondence (e.g. both components were rotated clockwise in one pattern and counterclockwise in the other) or in opposition (e.g. in one pattern one component was rotated clockwise, the other counterclockwise; the direction of rotation was reversed for each component in the second pattern). The results demonstrate that information from tuned pathways is not always used directly in making spatial judgments, but in some cases is combined across wide regions of the Fourier domain prior to the discrimination decision. We find two distinct patterns of combination that appear to independently signal information about texture and edges. These findings provide a potential link between low-level, spatially tuned analyzers in the visual system and higher-level pattern processing mechanisms.

Adult↗
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↗
PubMed1991

When orthogonal orientations are not processed independently.

We studied the extent to which two gratings, superimposed at orthogonal orientations, are processed independently in making spatial frequency discriminations. Our findings suggest that independence is not preserved in this task, and that it breaks down in two distinct ways: (1) judgments about one component are reduced in accuracy by the presence of the second; and (2) information about the two component gratings is not used independently in making judgments about the compound stimulus formed by them. These results place constraints on the applicability of models that assume information from spatially tuned mechanisms is directly available in performing a discrimination task.

Cues↗
PubMed1990

Cue summation in spatial discriminations.

We investigated the extent to which discrimination performance improves when more than a single cue distinguishes two patterns. When two simple gratings differ slightly in spatial frequency, orientation, and/or contrast, the performance of most observers is better in multiple-cue conditions than in single-cue conditions and by an amount indicating Euclidean summation of information. These results are shown to be consistent with discrimination models that integrate information over different, spatially selective pathways. However, little summation is found when the task requires integration of cues across widely separated spatial frequency bands. This result implies that information is integrated only over pathways tuned to a common region of the spatial frequency domain.

Contrast Sensitivity↗
PubMed1989

The statistical analysis of concurrent detection ratings.

The concurrent detection task is a powerful method for assessing interactions in the processing of two sensory signals. On each trial, a stimulus is presented that is composed of one, both, or neither signal, and the observer makes a detection rating for each stimulus. A classical bivariate signal-detection analysis applies to these data, but is limited by its inability to differentiate certain types of sensory interactions from more cognitive components, and by the lack of an associated testing procedure. The present paper presents an alternative analysis, based on the contingency table of sensory ratings. Six classes of effect can be distinguished and tested: (1) simple response bias, (2) detection of the two signals, (3) interference of each signal on the response to the other signal, (4) sensory and response correlation, (5) bivariate response biases, and (6) higher order association. Complete computational detail is provided.

Attention↗
PubMed1986

Widely separated spatial frequencies: mechanism interactions.

The question of independence between spatially tuned mechanisms that respond to very different frequencies is addressed by a theoretical reconstruction of their responses to single and compound grating stimuli presented at near-threshold levels. Parameters of sensory response distributions are estimated in a two-response rating experiment, and tested against those predicted by a Signal Detection model when independent processing is assumed. Small but consistent deviations from predicted values were observed and are interpreted in terms of frequency-specific patterns of inhibition and stochastic correlation. It is further demonstrated that these interactions may in part account for the superiority of discrimination over detection found with such widely separated frequencies.

Discrimination, Psychological↗
PubMed1985

Interactions between spatially tuned mechanisms: converging evidence.

Detection and identification performance is measured for four pairs of sinusoidal gratings that differ in spatial-frequency separation. A modified two-alternative forced-choice procedure (2 X 2) is used to measure performance on both tasks simultaneously. The results provide new evidence for the existence of interactions between tuned mechanisms that respond to widely separated frequencies. A method to compare data obtained in the 2 X 2 method quantitatively with both single- and double-response rating data is developed and used to compare the current data with previous rating results. The magnitudes of interactions isolated by the three procedures agree closely.

Attention↗
PubMed1981

Gratings: why frequency discrimination is sometimes better than detection.

Two models that assume independent processing among frequency-selective analyzers are presented. These are a distance model and an integration model derived from signal-detection theory. The models permit quantitative comparisons between detection and discrimination performance and lead to an empirical comparison that is sensitive to effects of correlated noise and interactions among the responding mechanisms. The stimuli were four pairs of sine-wave gratings that differed in spatial-frequency separation. They were presented to observers in a signal-detection rating paradigm, which was used for both detection and discrimination judgments. The results indicate the presence of properties, such as inhibitory interactions or correlated noise among responding mechanisms, that favor discrimination over detection.

Discrimination, Psychological↗