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PubMed2006

The spatiotemporal properties of visual completion measured by response classification.

A constant problem faced by the visual system is the identification of partly occluded objects within the visual scene. Recent experiments have demonstrated that the visual system engages in a process of visual completion, where the hidden parts of objects are filled into the visual representation. Recent experiments have also suggested that there may be a time course to this completion process. Here, we examined the spatiotemporal properties of visual completion by having observers classify figures defined by either luminance-defined or illusory contours and then correlating their decisions with externally added spatiotemporal visual noise. This "response classification" technique allowed us to derive a spatiotemporal correlation map (a "classification movie") that revealed the locations used by observers at each point in space and time during the stimulus presentation. We found that observers gradually became more influenced by noise at locations corresponding to illusory contours across the first 175 ms of stimulus presentation. Our results are consistent with the idea that there is a time course to the completion process on the order of approximately 175 ms.

Artifacts↗
PubMed1975

Psychopathology scale of the Hutt adaptation of the Bender-Gestalt Test: reliability.

The test-retest reliability of the Hutt Adaptation of the Bender-Gestalt test was explored with a population of 40 process schizophrenics over a two-week interval. The total Psychopathology Scale Score was found to have high retest reliability for both male and female patients (rho = .87 for males and .83 for females). Moreover the three major components for the Scale were found to have high reliability, and fairly high reliabilities were obtained for patients scoring high as well as low on the Scale. Interjudge reliability was also found to be very high (rho = .895), confirming previous studies in this respect. On these grounds, the Scale offers promise both for clinical and research purposes.

Adult↗
PubMedDate not supplied

Monocular patching in subjects with right-hemisphere stroke affects perceptual-attentional bias.

Monocular patching is a possible inexpensive treatment for spatial neglect. Previous studies were unpromising, but since neglect symptoms are heterogeneous, fractionating spatial bias may detect significant effects of patching. Poststroke, perceptual-attentional (PA) spatial bias, motor-intentional (MI) spatial bias, or both may occur. In this study, six poststroke subjects bisected lines while self-monitoring their performance via a camera/video apparatus. We dissociated PA and MI spatial bias by right-left reversing visual feedback in some trials. Subjects were tested with and without right and left eye patches. Patching did not affect group line-bisection error, but both right and left patches decreased individual subject PA spatial bias (p < 0.05). We detected no patching effect on individual subject MI spatial bias (significant patch side by bias interaction, p = 0.03). When we examined each subject's results separately, patching improved performance in subjects who had greater PA and MI spatial biases. We conclude that monocular patching may primarily affect poststroke PA spatial bias. Further studies on this intervention are needed.

Aged↗
PubMed2002

Gestalt grouping and common onset masking.

A four-dot mask that surrounds and is presented simultaneously with a briefly presented target will reduce a person's ability to identity that target if the mask persists beyond target offset and attention is divided (Enns & Di Lollo, 1997, 2000). This masking effect, referred to as common onset masking, reflects reentrant processing in the visual system and can best be explained with a theory of object substitution (Di Lollo, Enns, & Rensink, 2000). In the present experiments, we investigated whether Gestalt grouping variables would influence the strength of common onset masking. The results indicated that (1) masking was impervious to grouping by form, similarity of color, position, luminance polarity, and common region and (2) masking increased with the number of elements in the masking display.

Humans↗
PubMed2003

Moving and looming stimuli capture attention.

Attention capture is often operationally defined as speeded search performance when an otherwise nonpredictive stimulus happens to be the target of a visual search. That is, if a stimulus captures attention, it should be searched with priority even when it is irrelevant to the task. Given this definition, only the abrupt appearance of a new object (see, e.g., Jonides & Yantis, 1988) and one type of luminance contrast change (Enns, Austen, Di Lollo, Rauschenberger, & Yantis, 2001) have been shown to strongly capture attention. We show that translating and looming stimuli also capture attention. This phenomenon does not occur for all dynamic events: We also show that receding stimuli do not attract attention. Although the sorts of dynamic events that capture attention do not fit neatly into a single category, we speculate that stimuli that signal potentially behaviorally urgent events are more likely to receive attentional priority.

Adult↗
PubMed1999

Uniform connectedness and classical Gestalt principles of perceptual grouping.

We assessed whether uniform connectedness (UC; Palmer & Rock, 1994) operates prior to effects reflecting classical principles of grouping: proximity and similarity. In Experiments 1 and 2, reaction times to discriminate global letters (H vs. E), made up of small circles, were recorded. The small circles were respectively grouped by proximity, similarity of shapes, and by UC. The discrimination of stimuli grouped by similarity was slower than those grouped by proximity, and it was speeded up by the addition of UC. However, the discrimination of stimuli grouped by proximity was unaffected by connecting the local elements. In Experiment 3, similar results occurred in a task requiring discrimination of the orientation of grouped elements, except that the discrimination of stimuli grouped by UC was faster than that of those grouped by weak proximity. Experiment 4 further showed that subjects could respond to letters composed of discriminably separate local elements as fast as to those without separated local elements. The results suggest that grouping by similarity of shapes is perceived slower than grouping by UC, but grouping by proximity can be as fast and efficient as that by UC.

Adult↗
PubMed1997

Is visual image segmentation a bottom-up or an interactive process?

Visual image segmentation is the process by which the visual system groups features that are part of a single shape. Is image segmentation a bottom-up or an interactive process? In Experiments 1 and 2, we presented subjects with two overlapping shapes and asked them to determine whether two probed locations were on the same shape or on different shapes. The availability of top-down support was manipulated by presenting either upright or rotated letters. Subjects were fastest to respond when the shapes corresponded to familiar shapes--the upright letters. In Experiment 3, we used a variant of this segmentation task to rule out the possibility that subjects performed same/different judgments after segmentation and recognition of both letters. Finally, in Experiment 4, we ruled out the possibility that the advantage for upright letters was merely due to faster recognition of upright letters relative to rotated letters. The results suggested that the previous effects were not due to faster recognition of upright letters; stimulus familiarity influenced segmentation per se. The results are discussed in terms of an interactive model of visual image segmentation.

Adult↗
PubMed1987

Evaluating the visual-perceptual skills of children with cerebral palsy.

The Test of Visual-Perceptual Skills (TVPS) was used to determine if children with cerebral palsy demonstrated problems in visual perception on a motor-free visual perception test. Twenty-four children with cerebral palsy and 24 normal children, all of normal intelligence, were given the TVPS. Results showed that children with cerebral palsy attained significantly lower mean perceptual quotients than did the normal children. The TVPS appears to be a useful tool for the occupational therapist in evaluating visual perception in children with cerebral palsy.

Attention↗
PubMed1987

Strengths and weaknesses in the intellectual functioning of males with fragile X syndrome.

The intellectual strengths and weaknesses of 14 boys and young men with fragile X syndrome were assessed using the Sequential, Simultaneous, and Achievement domains of the Kaufman Assessment Battery for Children. Sequential processing, auditory, visual and motoric short-term memory, and arithmetic skills emerged as significant areas of weakness. Significant strengths were found in perceptual closure, inference, and flexibility. These findings both extend and contradict previous research and show the importance of classifying research groups by etiology of retardation rather than by overall level of impairment.

Achievement↗
PubMed1977

Sensory information and subjective contour.

The possibility that subjective contours are an artifact of brightness contrast was explored. In one experiment, inducing luminance was found to have different effects on the clarity of subjective contours and the magnitude of brightness contrast. The results of a second experiment indicated that differences of luminance in a stimulus display are necessary for subjective contours to be sustained, whereas chromatic differences are not. It is concluded that subjective contour and brightness contrast are distinct perceptual phenomena but share a dependency on the processing of edge information transmitted through the achromatic channels of the visual system.

Form Perception↗
PubMed1996

The development of perceptual completion abilities: infants' perception of stationary, partially occluded objects.

We explored infants' ability to perceive stationary, partially occluded objects as connected units (Experiments 1 and 2) with specific appearances (Experiment 3). In each experiment, the infants saw 2 test events involving what appeared to adults to be a tall rectangular object whose middle portion was hidden behind a narrow screen. During the test events, the screen alternately uncovered and covered the object. In Experiments 1 and 2, removal of the screen revealed either a single, connected rectangle (complete object event) or an interrupted rectangle with a gap where the screen had been (broken object event). In Experiment 3, removal of the screen revealed either a rectangle (rectangle event) or a cross-shaped object (cross-shape event). The pattern of infants' looking times at these events suggest that they perceive the unity of the partially occluded object by 6.5 months of age but did not perceive the form of the hidden part of the object until 8 months. The results of baseline control conditions support this interpretation.

Adult↗
PubMed1999

Parallel and competitive processes in hierarchical analysis: perceptual grouping and encoding of closure.

The role of perceptual grouping and the encoding of closure of local elements in the processing of hierarchical patterns was studied. Experiments 1 and 2 showed a global advantage over the local level for 2 tasks involving the discrimination of orientation and closure, but there was a local advantage for the closure discrimination task relative to the orientation discrimination task. Experiment 3 showed a local precedence effect for the closure discrimination task when local element grouping was weakened by embedding the stimuli from Experiment 1 in a background made up of cross patterns. Experiments 4A and 4B found that dissimilarity of closure between the local elements of hierarchical stimuli and the background figures could facilitate the grouping of closed local elements and enhanced the perception of global structure. Experiment 5 showed that the advantage for detecting the closure of local elements in hierarchical analysis also held under divided- and selective-attention conditions. Results are consistent with the idea that grouping between local elements takes place in parallel and competes with the computation of closure of local elements in determining the selection between global and local levels of hierarchical patterns for response.

Adult↗
PubMed1990

Perception of gated, highly familiar spoken monosyllabic nouns by children with and without learning disabilities.

A forward-gating procedure employing highly familiar monosyllabic words was used in auditory testing of age- and gender-matched children with learning disabilities and normally achieving children aged 8 to 11 years. The portion of the word presented, or "gate," was longer on each successive trial. Nondisabled children identified an average of one more word than the children with learning disabilities, but the mean duration required for word identification did not differ between groups. Better receptive vocabulary scores were associated with identification of words at shorter durations only among the children with learning disabilities. The two groups of children had similar numbers of different meaningful-word and different non-word incorrect responses. The children with learning disabilities exhibited poorer fine-grained auditory discrimination than a control group of nondisabled children. The study concluded that auditory closure skills for the gating task were as good among children with learning disabilities as among nondisabled children, but that sensory discrimination problems may contribute significantly to the learning difficulties of the former group.

Attention↗