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PubMed1990

Relative distance judgments of familiar and unfamiliar objects viewed under representatively natural conditions.

Carlson and Tassone (1971) reported that an object of familiar size viewed at an appreciable distance is perceived to be more distant than an unfamiliar object. Six experiments were designed to examine this effect. The results indicated that the effect is not dependent on Carlson and Tassone's method for assessing perceived relative distance; it occurs at some minimum viewing distance; it is unlikely to be caused by stimulus attributes confounded with the familiar versus unfamiliar size dichotomy; appears to be specific to judgments of the familiar object itself; and it does not occur if the familiar and unfamiliar objects have a common reference target. These findings are discussed with respect to the issue of whether familiar size influences perceived distance as distinct from influencing judgments of distance.

Adult↗
PubMed1990

Differential use of distance and location information for spatial localization.

Five experiments are reported in which subjects judged the movement or spatial location of a visible object that underwent a combination of real and induced (illusory) motion. When subjects attempted to reproduce the distance that the object moved by moving their unseen hands, they were more affected by the illusion than when they pointed to the object's perceived final location. Furthermore, pointing to the final location was more affected by the illusion when the hand movement began from the same position as that at which the object initially appeared, as compared with responses that began from other positions. The results suggest that people may separately encode two distinct types of spatial information: (1) information about the distance moved by an object and (2) information about the absolute spatial location of the object. Information about distance is more susceptible to the influence of an induced motion illusion, and people appear to rely differentially on the different types of spatial information, depending on features of the pointing response. The results have important implications for the mechanisms that underlie spatially oriented behavior in general.

Adult↗
PubMed1990

Detection and discrimination of coherent motion.

When viewing a pair of bars defined by the difference of spatial Gaussian functions (DOGs), human observers can discriminate accurately the relative movements of the bars, even when they differ in spatial frequency. On each trial, observers viewed two brief presentation intervals in which a pair of vertically oriented DOGs moved randomly back and forth within a restricted range. During one interval, both bars moved in the same horizontal direction and by the same magnitude (correlated movements); in the other interval, their movements were uncorrelated. When discrimination accuracy is related to the simultaneous detection of two independent movements, it was found that, if observers can detect the movements of spatially separated bars, they can tell whether their relative movements are correlated. Performance remained remarkably accurate even when the two bars differed in spatial frequency by more than two octaves or were presented separately to the two eyes. Apparently, the accurate discrimination of coherent motion involves an efficient spatial integration of optical motion information over multiple spatial locations and multiple spatial scales.

Adult↗
PubMed1991

Visual processing of rotary motion.

Local descriptions of velocity fields (e.g., rotation, divergence, and deformation) contain a wealth of information for form perception and ego motion. In spite of this, human psychophysical performance in estimating these entities has not yet been thoroughly examined. In this paper, we report on the visual discrimination of rotary motion. A sequence of image frames is used to elicit an apparent rotation of an annulus, composed of dots in the frontoparallel plane, around a fixation spot at the center of the annulus. Differential angular velocity thresholds are measured as a function of the angular velocity, the diameter of the annulus, the number of dots, the display time per frame, and the number of frames. The results show a U-shaped dependence of angular velocity discrimination on spatial scale, with minimal Weber fractions of 7%. Experiments with a scatter in the distance of the individual dots to the center of rotation demonstrate that angular velocity cannot be assessed directly; perceived angular velocity depends strongly on the distance of the dots relative to the center of rotation. We suggest that the estimation of rotary motion is mediated by local estimations of linear velocity.

Adult↗
PubMed1997

Color search and visual field segregation.

Visual search for targets that combine color and shape features that are shared by distracting items can be conducted spatially in parallel. Experimental results show that parallel search for color/shape conjunctions is possible when the shapes chosen let observers segregate the spatially interspersed items into figure and ground and when, within the figure, the target differs from other items by a distinguishing color feature. Results of experiments that manipulate stimulus color suggest that adaptive mechanisms of color discrimination are used to detect targets within such a figure.

Color Perception↗
PubMed2000

Is there an interaction between perceived direction and perceived aspect ratio in stereoscopic vision?

In monocular vision, the horizontal/vertical aspect ratio (shape) of a frontoparallel rectangle can be based on the comparison of the perceived directions of the rectangle's edges. In binocular vision of a typical three-dimensional scene (when occlusions are present), this is not the case: Frontoparallel rectangles would be perceived in a distorted fashion if an observer were to base perceived aspect ratio on the perceived directions of the rectangle's edges. We psychophysically investigated stereoscopically perceived aspect ratios of frontoparallel occluding and occluded rectangles for various distances and fixation depths. We found that observers did not perceive the distortions that would be predicted on the basis of the above-mentioned comparison of the perceived visual directions of the edges of the rectangle. Our results strongly suggest that the mechanism that determines perceived aspect ratio is dissociated from the mechanism that determines perceived direction. The consequences of the findings for the Kanizsa, Poggendorff, and horizontal/vertical illusions are discussed.

Depth Perception↗
PubMed1998

[The role of local conjunction in the integration process of shape and color].

It is an open question how simple features are integrated in the attention spotlight. In this paper, we examined two opposing models for the integration process of shape and color. One is a local conjunction model in which simple features of shape and color are combined directly. The other is a whole conjunction model in which simple features of shape are integrated into the whole shape and then it is combined with color. In Experiment 1, we measured the time required to search for a target defined by a conjunction of shape and color for five subjects with changing coloring of the figures. The slope of the search function was gentler when corners of figures were colored (p < 0.01). In Experiment 2, we measured the time required to integrate shape and color of figures presented in rapid serial visual presentation (RSVP) for five subjects. The presentation time required to answer the correct combination was shorter when corners were colored (p < 0.01). These results support the local conjunction model.

Adult↗
PubMed2003

[The examination of attentional load theory by Stroop-like task].

Attentional-load theory (Lavie, 1995) states that task load determines whether task-irrelevant stimuli are processed semantically. In three experiments students were asked to perform a Stroop-like task. They named a centrally fixated target color, while ignoring the task-irrelevant stimulus, which was an incompatible, compatible or non-color word. When perceptual load (the number of target-like stimuli adjacent to the target) was increased, the Stroop-like effect was diminished, providing the evidence for early selection. However, when cognitive load (task demands for identical stimuli) was increased, the evidence for late selection was found. These results were inconsistent with the previous hypothesis that both kinds of task load similarly affect the attentional mechanism.

Adult↗
PubMed1994

Somatosensory processing abilities of very low-birth weight infants at school age.

OBJECTIVE: The purpose of this study was to examine the relationship between somatosensory processing abilities of children at school age and their earlier experiences in the intensive care nursery as very low-birth weight (VLBW) infants. METHOD: The subjects were 35 VLBW children at school age (20 girls, 15 boys) who were free of congenital deformity and developmentally appropriate for gestational age. The subjects were part of an ongoing longitudinal study. Birth weight, number of days supported by mechanical ventilation, and number of days in the neonatal intensive care unit were examined in relation to somatosensory functions. Somatosensory functions measured were manual form perception, kinesthesia, finger identification, graphesthesia, and localization of tactile stimuli. RESULTS: VLBW children were significantly different on all measures of somatosensory processing when compared with the standardization group. CONCLUSION: Further research on the VLBW infant's somatosensory functioning will add to the existing body of knowledge concerning development and guide practice. The finding that the infants in this study, who did not have therapy intervention, later presented diminished somatosensory functioning supports the need to develop measures of somatosensory development for use in assessments and treatment during all developmental phases.

Birth Weight↗
PubMed1976

Finding the relevant attribute of visual or auditory stimuli.

The stimuli in a simple attribute-identification task were geometric designs or their verbal descriptions. Presentation was visual or auditory, in a constant order or a mixed order that varied the serial position of the relevant dimension (the dimension providing the relevant attribute) on each trial. Constant-auditory problems whose relevant dimensions were first or last were solved better, while mixed-auditory problems were solved least well, and visual problems were solved best overall with no serial-position effects. However, the results of an experiment in which the stimuli were noun pairs suggest that visual presentation is advantageous only if it produces a nonverbal code from which subjects can recover attributes lost from their descriptions during rehearsal.

Acoustic Stimulation↗
PubMed2000

Word rhyming as a probe of hemispheric language dominance with functional magnetic resonance imaging.

OBJECTIVE: The goal of this study was to create a probe of hemispheric dominance for language using functional magnetic resonance imaging. BACKGROUND: Surgical candidates for anterior temporal lobectomy often undergo the Wada test to determine language laterality. The Wada test is invasive and cannot localize intrahemispheric language areas when surgical resection encroaches on eloquent cortex. We report the results of a stimulation paradigm that activates regions involved in motor language, language phonology, and visual word form perception. METHOD: Five right-handed healthy subjects underwent blood oxygen level-dependent functional magnetic resonance imaging. Subjects alternately viewed consecutive word pairs, indicating when the words rhymed, and consecutive pairs of line arrays, indicating when the arrays matched by responding "Yes" or "No" using a button box. RESULTS: Subjects performed both tasks with equivalent accuracy. Compared with the nonverbal control task, word rhyming produced greater left-hemisphere activation than right-hemisphere activation. Foci of rhyme-related activation were found in the left Brodmann's area (BA) 44 (Broca's area), left dorsolateral prefrontal cortex (BA 9/46 and BA 8/9), left middle temporal gyrus (BA 22), and left fusiform gyrus (BA 37) in the posterior basal temporal lobe. Activation associated with the control task was present in the right parietal area and in right temporal and left parietal regions. CONCLUSIONS: Subvocal word rhyming activates dominant perisylvian cortical regions and may be useful for determining hemispheric language dominance and for functional mapping of language cortex.

Adult↗
PubMed2001

Interaction of scale and time during object identification.

On each trial a target object and a fragment of the target (or a control stimulus) were presented briefly enough to be integrated together. The stimuli were masked, and identification accuracy was measured. The fragments were large or small in size scale, and were presented early in processing (fragment before target) or late in processing (fragment after target). When presented early, large-scale fragments tended to facilitate identification more than small-scale fragments, but when presented late, small-scale fragments facilitated more than large-scale fragments. Facilitation effects from common feature fragments supported the idea of a spatiotemporal dependency, in which the efficiency of processing a piece of information depends on other pieces of information that have been processed. This is a strong type of global-to-local processing and can be interpreted within a structural description framework.

Analysis of Variance↗