Selective spatial attention and length representation in normal subjects and in patients with unilateral spatial neglect

The aim of this study was to assess whether perceptual representation along the horizontal axis is affected by hemispace position of the stimulus or by orienting attention to one side. Ten control subjects and 10 right brain damaged patients with left unilateral spatial neglect (USN) were asked to bisect lines of five lengths in three space positions (left, center, right) and under three cueing conditions (no cue, left cue, right cue). Normal controls showed significant displacement of bisection opposite to the side of hemispace presentation and toward the side of cueing. USN patients showed a bisection error toward the right end which increased with lines placed in the left hemispace and decreased with lines placed in the right hemispace and when attention was oriented toward the left side. We conclude that (1) In absence of cues normal subjects tend to overestimate the portions of space closer to their body midline; (2) both normal and USN patients tend to overestimate portions of space that they direct their attention to; (3) USN patients' performance without cueing is consistent with an attentional shift toward the right hemispace implying a gradient of overestimation of the right-most portions of space. A common neural substratum for directing attention and space representation can explain these findings.     

Memory for internally generated words in Alzheimer-type dementia: breakdown in encoding and semantic memory

The "generation effect" is a phenomenon in which words that are generated by the subject are remembered better than words which are read. The present experiments examined this effect in patients with mild-to-moderate dementia of the Alzheimer type (DAT), healthy elderly adults, and young adults under a variety of different encoding and retrieval conditions. Experiment 1 employed an intentional learning task with multiple study/test trials using the same list of words. While both the young and elderly adults exhibited higher recall for internally generated words than read words, the DAT patients failed to demonstrate the effect even after repeated exposures to the same stimulus list. Experiment 2 replicated this same pattern of results using an incidental learning paradigm with both recall and recognition tests. Various explanations as to why the DAT patients failed to show the generation effect were discussed with particular emphasis placed on the role of semantic memory and encoding failure.     

Response to commentaries on “A neurobiological model for near-death experiences”

This work has received financial support from FONDECYT (Project 1111-88). The authors also acknowledge the helpful comments of Dr. Bruce Cassels.     

On the development of procedural knowledge

Amnesic patients demonstrate by their performance on a serial reaction time task that they learned a repeating spatial sequence despite their lack of awareness of the repetition (Nissen & Bullemer, 1987). In the experiments reported here, we investigated this form of procedural learning in normal subjects. A subgroup of subjects showed substantial procedural learning of the sequence in the absence of explicit declarative knowledge of it. Their ability to generate the sequence was effectively at chance and showed no savings in learning. Additional amounts of training increased both procedural and declarative knowledge of the sequence. Development of knowledge in one system seems not to depend on knowledge in the other. Procedural learning in this situation is neither solely perceptual nor solely motor. The learning shows minimal transfer to a situation employing the same motor sequence.     

Effect of backward priming on word recognition in single-word and sentence contexts

Backward priming was investigated under conditions similar to those used in lexical ambiguity research. Subjects received prime-target word pairs that were associated either unidirectionally (BABY-STORK) or bidirectionally (BABY-CRY). In the first experiment, targets were presented 500 ms following the onset of visual primes, and subjects made naming or lexical decision responses to the targets. Forward priming was obtained in all conditions, while backward priming (i.e., priming for pairs in which there was a unidirectional target-to-prime association, as in BABY-STORK) occurred only with lexical decision. In the second experiment, primes were presented auditorily, either in isolation or in a sentence. Targets followed the offset of the primes either immediately or after 200 ms. Backward priming occurred with both response tasks, but only when the prime was an isolated word. In addition, backward priming decreased over time with the naming task, but not with lexical decision. These results suggest that the locus of the backward priming effect is different for the two response tasks. Further, the lack of a backward priming effect with sentence contexts suggests that backward priming cannot account for the demonstrations of multiple access in the lexical ambiguity literature. These results, therefore, support a context-independent view of lexical access.     

Insight without awareness: On the interaction of verbalization, instruction and practice in a simulated process control task

Four experiments in which subjects learned to control two versions of a complex simulated process control task show that verbalizable knowledge of procedures used to perform these tasks is very limited and is acquired late in learning. Individual learning curves associated with these tasks showed sudden improvements in performance, which were not accompanied by a similar increase in verbalizable knowledge. It was also found that verbal instructions consisting of exemplar memorization, strategies for rule induction, simple heuristics, and experts' instructions were all effective in enhancing novice subjects' performance. A theoretical framework is proposed in which subjects draw on two separate but interacting knowledge structures to perform these tasks. One knowledge structure is based on memory for past experiences (close analogies), and the other is based on one's current mental model of the task. Implicit sets of competing rules that control response selection are derived from both sources of knowledge. It is suggested that dissociations between task performance and verbalizing occur because memory-based processing tends to have more control over response selection because of its greater specificity, whereas a mental model tends to be the preferred mode for verbal reporting because of its greater accessibility.     

Parts of visual objects: an experimental test of the minima rule

Three experiments were conducted to test Hoffman and Richards's (1984) hypothesis that, for purposes of visual recognition, the human visual system divides three-dimensional shapes into parts at negative minima of curvature. In the first two experiments, subjects observed a simulated object (surface of revolution) rotating about a vertical axis, followed by a display of four alternative parts. They were asked to select a part that was from the object. Two of the four parts were divided at negative minima of curvature and two at positive maxima. When both a minima part and a maxima part from the object were presented on each trial (experiment 1), most of the correct responses were minima parts (101 versus 55). When only one part from the object--either a minima part or a maxima part--was shown on each trial (experiment 2), accuracy on trials with correct minima parts and correct maxima parts did not differ significantly. However, some subjects indicated that they reversed figure and ground, thereby changing maxima parts into minima parts. In experiment 3, subjects marked apparent part boundaries. 81% of these marks indicated minima parts, 10% of the marks indicated maxima parts, and 9% of the marks were at other positions. These results provide converging evidence, from two different methods, which supports Hoffman and Richard's minima rule.     

Type A behaviour and psychological androgyny among Greek college students

Research conducted primarily in the United States suggests that the combination of Type A behaviour, high instrumentality, and low expressiveness may place individuals at relatively high risk for coronary-artery and heart disease. The present research investigates the trans-societal generalizability of the structure, reliability, relationships among, and distributional characteristics of these measures for 117 college students in Athens, Greece. As hypothesized, the Greek students were significantly less instrumental and less expressive than the American students, and scored significantly higher on the measure of Type A. Although there were significant mean differences between these samples, the results suggest that many of the interscale relationships are comparable, supporting an etic (universal) interpretation of the findings. Nevertheless, the results suggested several emic (unique) characteristics of these measures and their interrelationships.     

Potential for hostility and dimensions of anger

Recent reviews have linked Potential for Hostility derived from the Structured Interview (SI) to coronary artery disease, independent of the global Type A pattern. The present study examined the construct validity of Potential for Hostility ratings by correlating Potential for Hostility with 21 scales from four widely used anger/hostility measures: 7 scales from the Anger Self-Report, 8 scales from the Buss-Durkee Hostility Inventory, the total score from the Novaco Anger Inventory, and 5 scales from the Multidimensional Anger Inventory. The pattern of correlations revealed that Potential for Hostility was significantly related to scales reflecting awareness and arousal of anger, particularly the verbal expression of anger. To identify underlying anger dimensions, the 21 scales were factor-analyzed. Examination of two and three rotated principal components confirmed previous solutions. The first component, representing anger-arousing and -eliciting situations and anger awareness, was labeled Experience of Anger. The second component, consisting of scales dealing with either physical assault or verbal expression of anger, was labeled Expression of Anger. When a third factor was retained, it contained scales of suspicion, mistrust-suspicion, and guilt: It was therefore labeled Suspicion-Guilt. Potential for Hostility was correlated only with the Expression of Anger factor in the two-factor solution; in the three-factor solution, Potential for Hostility was correlated equally with the Experience of Anger and Expression of Anger factors but was not correlated with the Suspicion-Guilt factor. The implications of these results for the assessment of hostility are discussed.