Biomedical subjects

Harold Pashler

Publications and source records attributed to Harold Pashler.

4 recordsLinked to original sources

PubMed2003

Multitasking costs in close-head injury patients. A fine-grained analysis.

The issue of whether severe close-head injury (CHI) patients suffer from disproportionate dual-task deficits compared with matched controls was investigated in two experiments. In the first experiment, either one or three masked letters were presented at the center of a monitor, followed by a pure tone at variable stimulus-onset asynchronies (SOAs). In half of the blocks of trials, the task on the letters required a delayed report of the letters at the end of each trial; in the other half of the blocks, the letters had to be ignored. The tone task always required an immediate manual response based on the tone pitch. In the second experiment, either three masked letters or three masked digits were presented with equal probability in each trial, followed by a tone at variable SOAs. The task required the delayed report of the characters only if they were letters, or ignoring the characters if they were digits. In both experiments, CHI patients and matched controls both exhibited an SOA-locked slowing of the reaction time (RT) to the tone: When characters had to be encoded for delayed report, tone RT increased progressively as SOA was decreased. The SOA effect on tone RT was more pronounced for CHI patients than for controls, suggesting that a substantial component of the slower processing time for CHI patients was related to a selective increase at a central stage of processing shared by the two tasks. Implications for models of the CHI effects on human performance are discussed.

Acoustic Stimulation↗

PubMed2002

Symmetry detection and visual attention: a "binary-map" hypothesis.

Recent research suggests that human symmetry-detection mechanisms cannot simultaneously compare different colors across the axis of symmetry (Nature 399 (1999) 115). In the present study, observers were required to judge symmetry in arrays composed of elements varying not only in color, but also in size, spatial frequency and orientation. In every case, response times increased with the number of different levels of a given feature. It is proposed that this increase reflects a sequential strategy whereby coarse "binary maps" are created by attentional filtering, and the symmetry of each map is then checked. Experiment 2 required observers to detect "pseudo-symmetry" (symmetry in feature values defined relative to an arbitrary featural boundary); the ease with which this task was accomplished supported the binary map hypothesis. The results suggest that (1) symmetry detection is spatially imprecise, and (2) attentional gating can operate prior to symmetry detection in the visual pathway.

Adult↗

PubMed2002

Volatile visual representations: failing to detect changes in recently processed information.

Research documenting people's inability to detect large changes in visual scenes suggests that visual representations may be sparse and volatile, providing no cumulative record of the attended items in a scene. However, these studies have failed to control for attention. Thus, the visual system may construct a cumulative record of all attended stimuli and still miss such changes, because they involve items that were never attended to. In two experiments, subjects saw 12-digit arrays and identified either the highest digit in the array (Experiment 1) or the lowest digit not in the array (Experiment 2). Subsequent change-detection tasks revealed that subjects often failed to detect changes that involved the same digits they had previously identified to perform the digit tasks successfully. This provides additional evidence that our usable visual representations are relatively impoverished and volatile.

Adult↗

PubMed2002

Central bottleneck influences on the processing stages of word production.

Does producing a word slow performance of a concurrent, unrelated task? In 2 experiments, 108 participants named pictures and discriminated tones. In Experiment 1, pictures were named after cloze sentences; the durations of the word-production stages of lemma and phonological word-form selection were manipulated with high- and low-constraint cloze sentences and high- and low-frequency-name pictures, respectively. In Experiment 2, pictures were presented with simultaneous distractor words; the durations of lemma and phoneme selection were manipulated with conceptually and phonologically related distractors. All manipulations, except the phoneme-selection manipulation, delayed tone-discrimination responses as much as picture-naming responses. These results suggest that early word-production stages--lemma and phonological word-form selection--are subject to a central processing bottleneck, whereas the later stage--phoneme selection--is not.

Adult↗