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PubMed1977

The effect of muscle function in discriminating thickness differences interocclusally and the duration of the perceptive memory.

The thresholds in discriminating the thickness differences interocclusally were measured with three different mouth openings on subjects having natural dentitions. Also the duration of the perceptive memory was studied. The results showed that the functional activation or fatiguing of masticatory muscles and the degree of mouth opening affect size discrimination interocclusally. The ability to perceive thickness differences between the incisors was more accurate after 1 hour's chewing than normally. The trend was significant with 0.5 mm and 10 mm mouth openings (2 P less than 0.01) and highly significant with an 20 mm mouth opening (2 P less than 0.001). With a 20 mm mouth opening (2 P less than 0.01) and 10 mm mouth opening (2 P less than 0.05) size discrimination was less accurate after two hours' fatiguing chewing than after one hour's conventional chewing. After 30 seconds' forceful isometric contraction and with 20 mm mouth opening discrimination was more accurate than normally (2 P less than 0.01). The trend was the same with a 10 mm mouth opening, but no difference could be observed when the mouth opening was 0.5 mm. The memory tests showed that with a 0.5 mm mouth opening thickness differences of 0.3-0.5 mm were most commonly correctly perceived twenty-four hours later, but when the mouth openings were 10 and 20 mm an interval of only 1 min between the reference and test piece trial impaired the performance.

Fatigue↗
PubMed2005

Perception time measured with the slope-transition paradigm (STP): category, set size, and task manipulations.

A perception time measure was obtained with the 'slope-transition paradigm' (STP), which is described in detail. In two experiments with the paradigm, participants viewed two sequential data frames, each presented for a wide range of durations. They made a binary response based on combined information from the two frames. The results showed piecewise linear response-time versus frame-duration functions with a slope-0 branch at short durations, followed by a slope-1 branch. The duration where the two branches met (the slope transition) was interpreted as the end of the perception of frame 1. For longer durations, the participant had completed the perception of frame 1 and was forced to waste time waiting for data from frame 2. In experiment 1, an odd-digit enumeration task was used, and set size and distractor category (even digits versus consonants) were varied. In experiment 2, a same/different task with digits was used and the type of judgment (literal versus parity) was varied. Perception time increased with set size. Distractor category and judgment type affected post-perceptual processes. The perception time measure of the STP is considered in relation to the attentional blink, repetition blindness, and object files.

Choice Behavior↗
PubMed2002

A new ecologically valid method to assess body size estimation and body size dissatisfaction.

OBJECTIVE: The primary aim of the present study was to develop an ecologically valid method for assessing the perception of body size (as opposed to the memory of body size). METHOD: Women with clinical eating disorders (N = 14) and no eating disorder (N = 24) estimated their actual and desired body size while looking in a mirror. Estimations were made using projected images that were the same height as the participants' reflections in the mirror. RESULTS: This new method assessed the perception of body size under conditions that resembled the real-life situation of viewing oneself in a mirror. Participants with eating disorders significantly overestimated their body size relative to controls (p <.05) and tended to be more dissatisfied with their body size (p =.07). DISCUSSION: It is argued that the new method assesses the perception of body size, is ecologically valid, and is the most clinically relevant of the methods developed to date.

Adult↗
PubMed2001

Envelope size tuning for stereo-depth perception of small and large disparities.

Stereopsis is the sense of depth derived from binocular disparities that are formed between targets that are matched between the two retinal images. Binocular matches for sustained stereopsis are based on similarity of orientation, spatial frequency and contrast of the two retinal images whereas matches for transient stereopsis depend on these parameters to a very limited extent. In this investigation we have tested the possibility that transient stereopsis forms matches between objects of similar overall size. The tuning of sustained and transient stereopsis to contrast-envelope size was investigated by presenting narrow-band Gabor targets of unequal size to the two eyes. Bandwidth for envelope-size tuning was estimated from the range of dichoptic size-differences over which stereo performance remained above chance level. An equal bandwidth of 2 octaves was found for the sustained and transient stereo systems when stimulated with parallel orientation Gabors that subtended a small disparity. Sustained-stereo performance with orthogonal carriers was reduced with large envelope sizes. Bandwidth of the transient stereo system increased to 3 octaves when tested with a larger disparity stimulus and it was independent of carrier orientation. Reducing the contrast of the larger-size Gabor improved transient-stereo performance from near chance (48-58%) to 85-95%. Thus the bandwidth for envelope-size tuning is much broader than indicated with equal physical contrast stimuli. The observed tuning to envelope size, while broad, is tighter than that observed for carrier spatial-frequency [Vis. Res. 38 (1998) 3057], carrier orientation [Vis. Res. 39 (1999) 2717] and contrast polarity [Vis. Res. 39 (1999) 4010] of the stimulus. Thus it would appear that envelope size and, to a greater extent, temporal synchrony of the dichoptic stimuli [Perception 24 (1995) 33] are the primary means for selecting matched binocular inputs for transient stereopsis.

Contrast Sensitivity↗
PubMed1991

Effects of preliminary information in a Go versus No-go task.

A series of studies using a Go versus No-go task examined the question of whether preliminary information available early in the recognition of a stimulus is made available to later processes before stimulus recognition is finished, a question relevant to the controversy between discrete and continuous models. Experiment 1 showed that a Go response is faster following a cue indicating that the response probably would be required than following a cue indicating it probably would not be required. Experiments 2-7 were conducted to find out whether analogous preparation occurred when probability of the Go response was signalled by easily discriminable features of a single stimulus rather than a separate cue. The effect was observed when the easily discriminable features uniquely determined the name of the stimulus letter, but not when they merely indicated that the stimulus name was one of two visually similar letters. These results are consistent with the Asynchronous Discrete Coding model, in which the perceptual system makes available to later processes only preliminary information corresponding to discretely activated stimulus attributes.

Attention↗
PubMed1988

Detection of visual stimuli after lesions of the superior colliculus in the rat; deficit not confined to the far periphery.

The visual neglect which follows lesions of the superior colliculus in the rat is well documented, although its nature has been somewhat contentious. Recently, using large, bright stimuli, Overton et al. [Exp. Brain Res., 59 (1985) 559-569] presented evidence that collicular lesions produce a detection deficit in the far peripheral visual field (120 degrees), whilst the central field is unaffected. However, some simple tests for visual neglect by other workers suggest that a detection deficit may also exist in the central field, if the stimuli are dim (and small). This possibility was investigated psychophysically. Using a signal detection paradigm, sensitivity to small (2.5 degrees v.a.), transient (modal duration 200 ms) stimuli of varying luminance was determined at 40 degrees on either side of the vertical meridian, before and after collicular lesions or control lesions of the striate cortex. Despite extensive preoperative training, collicular animals showed a decrease in sensitivity of around 50% for all stimulus intensities postoperatively. This deficit was significantly more severe than that produced by striate lesions. Furthermore, it proved very difficult to retrain the animals to a preoperative criterion. These data suggest that collicular lesions do indeed cause a detection deficit which is not confined to the far periphery, and that this deficit may specifically affect the detection of small stimuli. The proposed detection deficit is related to recent anatomical findings in the rat.

Animals↗
PubMed2005

Border ownership from intracortical interactions in visual area v2.

A border between two image regions normally belongs to only one of the regions; determining which one it belongs to is essential for surface perception and figure-ground segmentation. Border ownership is signaled by a class of V2 neurons, even though its value depends on information coming from well outside their classical receptive fields. I use a model of V2 to show that this visual area is able to generate the ownership signal by itself, without requiring any top-down mechanism or external explicit labels for figures, T junctions, or corners. In the model, neurons have spatially local classical receptive fields, are tuned to orientation, and receive information (from V1) about the location and orientation of borders. Border ownership signals that model physiological observations arise through finite range, intraareal interactions. Additional effects from surface features and attention are discussed. The model licenses testable predictions.

Algorithms↗
PubMed1992

Skilled reaching in rats and humans: evidence for parallel development or homology.

Forelimb reaching by the rat is used as a paradigm for the experimental study of neural control, plasticity, and recovery of function after injury, in the expectation that results are generalizable to humans. The present study was done to compare rat to human reaching movements. The movements of both species were videorecorded and subjected to frame-by-frame analysis using Cartesian (spatial and velocity) and Eshkol-Wachman Movement Notation (EWMN) systems. The component movements of reaching, their sequence and velocity profiles, and their topography were similar in the two species. Both species also displayed more supination and lengthened grasping times when reaching for small as opposed to large objects. Both rats and humans moved the limb medially using the upper arm to aim it when they were required to reach through an aperture but in a free reaching test only rats continued to aim the limb. Human movements were characterized by greater blending of movement components, more variability, and independent digit use. Arguments are presented that the similarities and differences in rat and human reaching are not trivially accounted for by limb and task similarities. The many similarities in the movements of the two species provide evidence for at least parallel development or perhaps even homology.

Adult↗
PubMed1983

Imagery paradigms: how vulnerable are they to experimenters' expectations?

The effects of experimenters' expectations on subjects' responses in imagery paradigms were investigated by leading some experimenters to believe that performance based on the use of imagery would be superior to performance based on perception. Other experimenters were led to expect perceptual superiority. Three paradigms are tested. Experiment 1 considered imaginal and perceptual acuity as functions of the size and relative brightness of the stimulus patterns; Experiment 2 compared imaginal and perceptual scanning of maps; and Experiments 3 and 4 studied the identification of rotated hands after imaginal or perceptual priming. In all the experiments, subjects' performances varied with the experimenters' beliefs, suggesting that these paradigms are sensitive to subtle influences from experimenters' tacit, unintentional cues. Experiment 4 probed the ability of observers to identify both tacit cues and the experimenters' expectations. The observers accurately assigned the experimenters' beliefs but were unable to systematically detect distinguishing and differential characteristics of the experimenters' presentations of the instructions. Analysis of taped transcriptions yielded some differences in temporal phrasing. Implications of these results are discussed.

Discrimination Learning↗
PubMed1993

Reaction time drifts identify objects of attention in pigeon visual search.

Three pigeons searched for a unique target form among 31 identical distractors, and search reaction time (RT) was measured. Within experiments, target and distractor on each trial were drawn from the same small set of forms that differed from each other by simple features. Correlations across sessions among RTs to the various form pairs were analyzed. Experiment 1 indicated drifts of attention between the top of the forms, where a gap might appear, and the bottom, where a line might appear, and also suggested drifts of attention to the line as a target feature. Experiment 2 indicated similar drifts between the top and bottom of the forms and between small differences and large differences in target features. Attention to intraform location appeared relatively independent of attention to target features. The method provides a new way to identify functionally separable aspects of stimulus processing and to describe their temporal properties.

Animals↗
PubMed1989

Wide-angle memories of close-up scenes.

We report a picture-memory phenomenon in which subjects' recall and recognition of photographed scenes reveal a pronounced extension of the pictures' boundaries. After viewing 20 pictures for 15 s each, 37 undergraduates exhibited this striking distortion; 95% of their drawings included information that had not been physically present but that would have been likely to have existed just outside the camera's field of view (Experiment 1). To determine if boundary extension is limited to recall and drawing ability, Experiment 2 tested recognition memory for boundaries. Eighty-five undergraduates rated targets and distractors on a boundary-placement scale. Subjects rated target pictures as being closer up than before and frequently mistook extended-boundary distractors as targets. Results are discussed in terms of picture comprehension and memory. In addition to its theoretical value, discovery of the phenomenon demonstrates the importance of more widespread use of open-ended tests in picture-memory methodology.

Adult↗
PubMed2004

Visual estimation of spatial requirements for locomotion in novice wheelchair users.

Locomotion using a wheelchair requires a wider space than does walking. Two experiments were conducted to test the ability of nonhandicapped adults to estimate the spatial requirements for wheelchair use. Participants judged from a distance whether doorlike apertures of various widths were passable or not passable. Experiment 1 showed that participants underestimated the spatial requirements for wheelchair use but overestimated the spatial requirements for walking. Experiment 2 showed that their underestimation improved but was not completely eliminated after 8 days of practice passing through apertures. Analyses of wheelchair performance in the practice condition showed that the underestimation may have arisen from misperception of the positions of the hands when the participants were grasping the wheelchair hand-rims. The theoretical and practical implications of these findings are discussed.

Adult↗
PubMed1990

Illusion reversal rate as a function of subjective depth.

Undergraduate students (N = 48) served as subjects in a test of Gregory's theory of illusions. Twenty-four students made judgments about the subjective depth of three reversible illusions--Necker cube, Book, and Pyramid--under the conditions of complete versus incomplete illusions and illusions without depth cues versus with depth cues. An additional 24 subjects recorded the three illusion reversal rates under slightly altered conditions. Differences were found among the various illusions with respect to complete versus incomplete illusions, reversal rate, subjective judgments of depth, and certain correlation values. Support for Gregory's theory of illusion as displaced or misleading depth perception is offered by these results.

Adolescent↗
PubMed1992

The representation of objects and their attributes in memory: evidence concerning memory for location.

The general principle is advanced that different attributes of objects (e.g. shape and colour) are more readily associated when they are attributes of the same object than when they are attributes of different objects. Previous studies provide support for the principle, for they have shown that a shape is more readily associated with its own colour than, for example, with the colour of its background. In the present experiments, the principle was applied to the attributes of shape and location. In four experiments it was shown that a shape was more readily associated with its own location than with the location of another object. Differences in contiguity between the presentation of the shape and the location with which the shape was to be associated were controlled for, as were other factors. The results were interpreted as providing support for the general principle stated above. It was suggested that the general principle could be explained by supposing that memory is propositional in format.

Adult↗