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Biomedical subjects

H R Schiffman

Publications and source records attributed to H R Schiffman.

12 recordsLinked to original sources
PubMed1990

Semantic context and figure-ground organization.

The semantic-priming paradigm was used to investigate the effect of semantic context on the latency to identify visually ambiguous and unambiguous targets. Ambiguous targets had reversible figure-ground organizations analogous to Rubin's vase-profiles picture in which the figural vase is shaped by the same contour that, if reassigned, shapes two figural profiles. The two organizations of the ambiguous targets were either a series of black irregular shapes or a familiar word in white letters; subjects were required to achieve the latter organization. Unambiguous target words were not reversible. Related primes, unlike unrelated primes, facilitated the identification of both types of target; but the magnitude of facilitation was greater for ambiguous targets. The results demonstrate that semantic context influences the speed of figure-ground organization and add perceptual ambiguity to the target manipulations that interact with context to affect encoding.

Adult↗
PubMed1986

Percutaneous drainage access: a simplified coaxial technique.

We describe an access technique that we have used in 150 nephrostomy and biliary drainage procedures and for access to some abscesses and viscera. The system provides safe coaxial access with a 22-gauge removable hub needle, which then acts as a guide wire and is replaced by an 18-gauge cannula. A major advantage is that only one guide wire is used (0.038-inch) for the entire drainage procedure. No significant complications have occurred to date with this method.

Biliary Tract Surgical Procedures↗
PubMed1978

The role of apparent depth and context in the perception of the Ponzo illusion.

The role of apparent depth features and the proximity of the test lines to the adjacent contours in the actuation of the Ponzo illusion was examined. Six versions of the Ponzo figure were employed: a standard Ponzo figure and five modified figures in which the test lines varied in orientation (horizontal or vertical) and in location (inside or outside the converging contours). Both manipulations resulted in a significant decrease in the magnitude of the illusion in comparison to the standard Ponzo figure. The results suggest that the Ponzo illusion is significantly affected by contextual factors.

Depth Perception↗
PubMed1978

Effect of perspective and slant on perception of apparent size and distance.

An experiement was performed to re-examine the role of linear perspective and floor slant on apparent size and distance scales. Misleading perspective cues did not alter the observers' apparent distance scales but did influence the absolute magnitude of distance judgments; floor slant exerted little influence on apparent distance scales or the absolute magnitude of distance judgments. Neither perspective nor slant manipulation reliably affected apparent size scales or exerted more than a minor influence on the absolute magnitude of size judgments.

Cues↗
PubMed1977

The perception of brief temporal intervals: power functions for auditory and visual stimulus intervals.

Two experiments were performed to examine the role of method of estimation and the employment of a standard stimulus on the judged duration of auditory and visual stimuli presented for brief temporal intervals (0.25 to 5.0 s). The results indicate that the relationship between judged and physical duration is nearly direct and linear. Psychophysical methodology and stimulus modality exerted little influence on the obtained power functions.

Acoustic Stimulation↗
PubMed1977

Contextual effects in duration experience.

The role of contextual factors on duration estimates was investigated, employing 6 time intervals ranging from 15 to 35 sec (demarcated by the onset and termination of a display panel of lights). When compared with earlier research, the results suggest that duration estimates are affected by the context of the stimulus intervals with regard to other stimuli in the series. Specifically, those stimuli that were overestimated when they were the shortest members of the series were underestimated when they were the longest intervals of the stimulus series. In addition, a lengthening effect was observed: duration estimates increased over blocks of trials for all stimulus intervals.

Discrimination, Psychological↗
PubMed1977

The role of number and familiarity of stimuli in the perception of brief temporal intervals.

The influence of stimulus number and familiarity on judged duration were investigated. The stimuli were slides with different numbers of stimulus elements of a familiar or unfamiliar nature. The task was to reproduce the durations of the slides, each shown for four intervals: 5, 9, 13, and 17 sec. The results show that the number of stimulus elements presented within a given interval affected its perceived duration, although the familiarity of those elements (as defined herein) did not. Finally, the shorter intervals sampled here were overestimated and the longer intervals were underestimated, thereby supporting Vierordt's law.

Humans↗
PubMed1976

The effect of minor tranquilizers on psychomotor performance.

The effect of a standard daily regimen of chlordiazepoxide, prazepam (a new benzodiazepine tranquilizer), and placebo were examined in a three way double-blind comparison for a sample of normal volunteers. The criteria include a limited spectrum of psychomotor functions. A learning effect was conspicuous for all drugs on all criteria during the day-long sequence of ten trials. For the most part the differences between the drug groups were insignificant, but there were distinctive modifications in the performance of the chlordiazepoxide group. The clearest effect of the tranquilizer medications was found in the time estimation tests. Paradoxically, the drugs correct a naturally occurring perceptual error.

Adult↗
PubMed1975

Depth perception in the rat (Rattus Norvegicus): prepotency of three-dimensional over two-dimensional surfaces.

The descent behavior to two- and three-dimensional surfaces in a depth situation was measured and compared for 45-50 days-old hooded rats. When depth differences between surfaces were controlled, significantly more descents were made to three-dimensional than to the two-dimensional surface. The results suggest that a three-dimensional surface--more representative of an animal's natural terrain--provides a more informative environment for motion parallax than does a two-dimensional one.

Animals↗
PubMed1975

The role of figure orientation and apparent depth in the perception of the horizontal-vertical illusion.

An experiment was performed which examined the role of figural orientation directly, and the role of an inappropriately invoked size-constancy mechanism indirectly, in the actuation and magnitude of the horizontal-vertical illusion. When the vertical line of the stimulus figure was aligned above the horizontal line, the illusory effect was significant and positive; in contrast, when the vertical line was located below the horizontal line, the illusion was negative. Under the assumption that a vertical line can appear as a foreshortened line in depth, these findings support an explanation based on the operation of a misapplied size-constancy mechanism.

Depth Perception↗