Biomedical subjects

Mary M Conte

Publications and source records attributed to Mary M Conte.

4 recordsLinked to original sources

PubMed2005

Interaction of luminance and higher-order statistics in texture discrimination.

Most studies of texture processing are based on textures in which individual pixel statistics are varied and spatial correlations are absent ("IID textures"), or textures in which spatial correlation structure is varied and luminance, or first-order, statistics are held constant. Here we jointly examine simple pixel statistics and fourth-order spatial correlation structure along the continuum of "even" and "odd" isodipole textures of Julesz, Gilbert and Victor [Julesz, B., Gilbert, E.N., & Victor, J.D. (1978). Biological Cybernetics, 31(3) 137-140], as well as their interactions. Absolute efficiency to detect either kind of statistical cue is low: approximately 0.05 for luminance statistics, and 0.004 for isodipole statistics. Above threshold, isodipole statistics must change by approximately four times the amount that pixel statistics must change to generate an equally salient texture. When pixel statistics and isodipole statistics are simultaneously varied, the two texture cues combine by probability summation and perceptual distances are approximately Euclidean. Superimposed on this picture are subtle foreground/background asymmetries that suggest properties of the visual mechanisms that are sensitive to these image statistics.

Adult↗

PubMed2004

Local processes and spatial pooling in texture and symmetry detection.

We examined the ability of human observers to detect three kinds of statistical structure in binary arrays: first-order statistics (luminance), local fourth-order statistics (isodipole textures), and long-range statistics (bilateral symmetry). Performance was closest to ideal on the luminance task and furthest from ideal on the symmetry task. For each kind of statistic, the dependence of performance on the degree of structure was well described by a model consisting of an initial stage of multiple independent detectors, followed by a pooling stage. For the luminance task and the isodipole task, performance was well-modeled by local processing followed by extensive spatial pooling. For the symmetry task, limitations at the local detection stage and a near-absence of spatial pooling were needed to model for performance.

Adult↗

PubMed2004

Visual working memory for image statistics.

To define the role of statistical features of images in visual working memory, we compared the ability of subjects (N=6) to identify changes in arrays of black and white checks when these changes altered some aspect of their statistical structure, versus when these changes did not. Alteration of luminance statistics or local higher-order statistics improved performance, but alteration of the degree of bilateral symmetry did not. The dependence of performance on the degree of statistical change indicated that statistical information was represented in a graded, rather than categorical, fashion.

Adult↗

PubMed2002

Temporal phase discrimination depends critically on separation.

Temporal phase discrimination was measured as a function of spatial separation of the stimulus components. In contrast to many previous studies, phase discrimination thresholds were measured directly, rather than inferred from the ability to discriminate synchronous from antiphase stimuli, or from segregation or shape tasks. For abutting bars, relative phase thresholds were closely proportional to temporal frequency. The proportionality corresponded to a threshold temporal offset of 2.5-9.5 ms, across subjects. Introduction of a small gap (0.125 degrees or greater) led to a dramatic (3- to 7-fold) increase in thresholds for temporal phase discrimination, and thresholds were no longer proportional to temporal frequency. Insertion of a third bar filling the gap resulted in a recovery of the low thresholds, provided that its modulation was consistent with apparent motion across the three bars. Below 8 Hz, phase discrimination thresholds across three bars were equivalent to thresholds for two abutting bars. Above 8 Hz, phase discrimination thresholds for the three bar combination were lower than thresholds for two adjacent bars, implying that phase information was integrated across all three bars.Phase discrimination thresholds do not appear to reflect the properties of a single mechanism. Especially at high temporal frequencies, low thresholds for phase discrimination are closely tied to the presence of apparent motion. Temporal phase discrimination is markedly impaired by a small separation of stimulus components. Moreover, the inability to detect phase differences across gaps corresponds to the loss of phase-dependence of vernier acuity thresholds across gaps.

Adult↗