Biomedical subjects

Mary A Peterson

Publications and source records attributed to Mary A Peterson.

8 recordsLinked to original sources

PubMed2006

Independent representation of parts and the relations between them: evidence from integrative agnosia.

Whether objects are represented as a collection of parts whose relations are coded independently remains a topic of ongoing discussion among theorists in the domain of shape perception. S. M., an individual with integrative agnosia, and neurologically intact ("normal") individuals learned initially to identify 4 target objects constructed of 2 simple volumetric parts. At test, the targets were mixed with distractors, some of which could be discriminated from the targets on the basis of a mismatching part, whereas the rest could be discriminated only on the basis of the altered spatial arrangements of parts. S. M. learned to identify the target objects, although at a rate slower than that of the normal participants. At test, he correctly rejected distractors on the basis of mismatching parts but was profoundly impaired at rejecting distractors made of the same local components but with mismatching spatial arrangements. These results suggest that encoding the spatial arrangements of parts of an object requires a mechanism that is different from that required for encoding the shape of individual parts, with the former selectively compromised in integrative agnosia.

Adult↗

PubMed2005

Ordinal configural cues combine with metric disparity in depth perception.

Prior research on the combination of depth cues generally assumes that different cues must be in the same units for meaningful combination to occur. We investigated whether the geometrically ordinal cues of familiarity and convexity influence depth perception when unambiguous metric information is provided by binocular disparity. We used bipartite, random dot stereograms with a central luminance edge shaped like a face in profile. Disparity specified that the edge and dots on one side were closer than the dots on the other side. Configural cues suggested that the familiar, face-shaped region was closer than the unfamiliar side. Configural cues caused an increase in perceived depth for a given disparity signal when they were consistent with disparity and a decrease in perceived depth when they were inconsistent. Thus, geometrically ordinal configural cues can quantitatively influence a metric depth cue. Implications for the combination of configural and depth cues are discussed.

Cues↗

PubMed2005

EEG phase synchrony differences across visual perception conditions may depend on recording and analysis methods.

OBJECTIVE: (1) To investigate the neural synchrony hypothesis by examining if there was more synchrony for upright than inverted Mooney faces, replicating a previous study; (2) to investigate whether inverted stimuli evoke neural synchrony by comparing them to a new scrambled control condition, less likely to produce face perception. METHODS: Multichannel EEG was recorded via nose reference while participants viewed upright, inverted, and scrambled Mooney face stimuli. Gamma-range spectral power and inter-electrode phase synchrony were calculated via a wavelet-based method for upright stimuli perceived as faces and inverted/scrambled stimuli perceived as non-faces. RESULTS: When the frequency of interest was selected from the upright condition exhibiting maximal spectral power responses (as in the previous study) greater phase synchrony was found in the upright than inverted/scrambled conditions. However, substantial synchrony was present in all conditions, suggesting that choosing the frequency of interest from the upright condition only may have been biased. In addition, artifacts related to nose reference contamination by micro-saccades were found to be differentially present across experimental conditions in the raw EEG. When frequency of interest was selected instead from each experimental condition and the data were transformed to a laplacian 'reference free' derivation, the between-condition phase synchrony differences disappeared. Spectral power differences were robust to the change in reference, but not the combined changes in reference and frequency selection criteria. CONCLUSIONS: Synchrony differences between face/non-face perceptions depend upon frequency selection and recording reference. Optimal selection of these parameters abolishes differential synchrony between conditions. SIGNIFICANCE: Neural synchrony is present not just for face percepts for upright stimuli, but also for non-face percepts achieved for inverted/scrambled Mooney stimuli.

Adult↗

PubMed2005

The edge complex: implicit memory for figure assignment in shape perception.

Viewing a stepped edge is likely to prompt the perceptual assignment of one side of the edge as figure. This study demonstrates that even a single brief glance at a novel edge gives rise to an implicit memory regarding which side was seen as figure; this edge complex enters into the figure assignment process the next time the edge is encountered, both speeding same-different judgments when the figural side is repeated and slowing these judgments when the new figural side is identical to the former ground side (Experiments 1A and 1B). These results were obtained even when the facing direction of the repeated edge was mirror reversed (Experiment 2). This study shows that implicit measures can reveal the effects of past experience on figure assignment, following a single prior exposure to a novel shape, and supports a competitive model of figure assignment in which past experience serves as one of many figural cues.

Cues↗

PubMed2004

Amodal completion in visual search: preemption or context effects?

In a previous study, search for a notched-disk target abutting a square among complete-disk nontargets and squares was inefficient in 250-ms exposures, but relatively efficient in 100-ms exposures. This finding was interpreted as evidence that amodal completion proceeds through a mosaic and then a completion stage, with the latter preempting the former. We used the same target but changed its context: Nontargets were instead notched disks near squares. Task set was also different: Participants searched for a complete disk. Contrary to the prediction of the preemption model, search was efficient in the 100-ms condition and inefficient in the 250-ms condition. We propose that in both the present and the previous studies, the target was ambiguous, and task set and context affected how it was perceived. In both experiments, set effects were evident for 100-ms exposures; context effects were evident for 250-ms exposures.

Affect↗

PubMed2003

Implicit memory for novel figure-ground displays includes a history of cross-border competition.

When configural cues specify that a figure lies on opposite sides of a repeated border in prime andprobe shapes, probe latencies are longer than when prime and probe borders are unrelated. Do such results reflect negative priming for the shape of the prime ground or cross-border competition from figure memory? The present study tested these alternatives by adding partial closure as a competing cue and reducing the similarity between the prime ground and the shape of the probe. Results supported the cross-border competition interpretation. Additional findings were that partial closure is a configural cue and that response effects can emerge from the potential shape on the ground side of a border. One prior experience was sufficient for these effects.

Competitive Behavior↗

PubMed1991

Directing spatial attention within an object: altering the functional equivalence of shape descriptions.

Three experiments extended the demonstrated effects of spatial attention to a new area, the perceptual organization of objects. We manipulated observers' fixation location, their spatial attention location, and their intentions to hold one alternative of a Necker cube that had been altered in one region to favor one of the alternative interpretations (the biased region) and measured reports about the perceived organization of the cube over 30-s trials. Regardless of fixation location, responses showed obligatory effects of the bias only when observers attended to the biased region of the cube and not when they attended to the unbiased region of the cube, even when the biased region lay between fixation and the attended unbiased region. On the basis of these experiments, we argue that spatial attention operates through mechanisms of facilitation and inhibition to determine the functional nature of the structural description of an object.

Adult↗

PubMed1986

Illusory concomitant motion in ambiguous stereograms: evidence for nonstimulus contributions to perceptual organization.

Three experiments were performed to test whether perceptual organization is cognitively or motivationally penetrable. In Experiments 1 and 2, subjects viewed a reversible stereogram while instructed to hold one depth organization. Responses about depth were recorded indirectly by recording responses about direction of the illusory concomitant motion that is perceptually coupled to depth in a stereogram. Inasmuch as perceptually coupled variables covary without necessary stimulus covariation, a post-perceptual locus for any intention effects they exhibit is unlikely. Experiments 2 and 3 examined the possibility that instructed intention might influence perception indirectly by influencing eye movements: Viewers' vergence position was measured directly through responses about alignment of a vernier nonius fixation. In all three experiments, a residual effect of instructed intention was found. Therefore, instructed intention may influence perceptual organization by influencing internal nonstimulus components integral to the perceptual process.

Adolescent↗