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Biomedical subjects

H S Hock

Publications and source records attributed to H S Hock.

11 recordsLinked to original sources
PubMed1992

The effects of common movement and spatial separation on position- and motion-based judgements of relative movement.

When common movement is superimposed on relative movement (changes in separation between two dots), relative movement thresholds increase nonlinearly as a function of initial dot separation. For large separation (greater than 2.0 deg), thresholds increase gradually with increased separation. It is shown that this reflects judgments based on perceived relative motion. For small separations (less than 2.0 deg), thresholds increase sharply with increased separation. It is shown that this reflects judgments based on perceived changes in relative position. Evidence is presented that superimposed common movement reduces sensitivity to relative movement by reducing sensitivity to relative motion. This provides a "window", in the range of small dot separations, for relative movement judgements to be based on the perception of changes in relative position, even though motion is perceived for individual dots.

Humans↗
PubMed1989

Evidence for the abstractive encoding of superficial position information in visual patterns.

When presented a series of patterns inside a frame, subjects unintentionally retained information concerning the frame-relative location of the elements composing the patterns; they could use this superficial information to estimate the frequency with which the elements occurred at various locations within the frame. There were two aspects of the results that supported the hypothesis that this superficial element-location information was abstractively encoded and, therefore, retrievable independent of the patterns comprising the elements: (1) Correlations between actual and estimated frequency remained significant after the effects of pattern recall were partialled out, and (2) correlations were enhanced by assuming that the frequency estimate for each location was affected by the imprecise coding of position for elements falling in surrounding locations. Additional experiments indicated that an orienting task emphasizing pattern recall resulted in very inaccurate estimation of element-location frequency, and intentional instructions improved the precision of position coding for individual elements.

Adult↗
PubMed1988

Perceptual units in the acquisition of visual categories.

A series of experiments provided evidence that the representational structure of categories comprising dot patterns is based on pattern parts and pattern configuration rather than on pattern elements. We found that similarity judgments and postacquisition classification data could not be explained in terms of element-level perceptual units, even for categories of dot patterns with seven of their eight dots in the exact same relative location. The importance of higher order perceptual units was indicated by evidence that the long-term retention of information specific to previously learned category exemplars, which is typical of natural objects, can also be obtained for artificial dot patterns, providing their structure reflects the perceptual characteristics identified in Tversky and Hemenway's (1984) study of natural objects: Members of the same category had to be perceptually distinctive at the level of pattern configuration and perceptually similar at the level of pattern parts. The level of within-category similarity for a set of categories (relative to between-categories similarity) did not predict whether item-specific information would be retained; long-term retention appears to require both within-category similarity and dissimilarity, but at different levels of perceptual structure.

Attention↗
PubMed1986

Frequency discrimination: assessing global-level and element-level units in memory.

Subjects' knowledge of how often various events occur was used to assess the retention of memory units for word-like strings of letters. A series of strings was presented at one of three exposure durations. Within the series, the frequencies of occurrence of different strings and of the letters composing the strings were varied orthogonally. At relatively long exposure durations, subjects could discriminate the frequency of occurrence for both strings and their constituent letters. The formation of global-level (string) memory units was indicated by judgments of string frequency being unaffected by either the frequencies of their component letters or experimental conditions (brief exposures) that prohibited accurate judgment of letter frequency. Although judgments of letter frequency were sometimes biased by the frequency of the strings containing the letters, the success with which the judgments discriminated different levels of letter frequency did not depend on the activation of string-level memory units. Furthermore, subjects' frequency judgments for letters were not predictable from their recall of the strings containing the letters. These results, which could not be explained by Tversky and Kahneman's (1973) "availability heuristic," provided evidence for the formation of element-level (letter) memory units. A converging experiment established that element-level frequency information could be abstracted from words as well as nonwords, and further, that this information was stored in long-term memory.

Adolescent↗