The role of position in object selection in vision

Summary Within contemporary visual-information-processing psychology, two classes of selective-attention theories can be distinguished: position-not-special theories and position-special theories. The position-not-special theories postulate that attentional selection by colour, by form, and by position are equivalent selective operations. The position-special theories assume that selection by position is more basic or direct than selection by colour or by form. Examples of both types of theory are briefly described, and irrelevant and relevant evidence is critically discussed. It is concluded that the relevant evidence is directly compatible with the position-special views and that the position-not-special theories require additional extraneous assumptions. The position-special model presented in Van der Heijden (1992) is elaborated in further detail. It is shown that this model is compatible with two important and often substantiated assumptions of the position-not-special theories: the assumption that pre-attentive analysers organize the visual scene in objects against a background, and the assumption that visual-selective attention can be directed at objects isolated in this way. This position-special theory is a parsimonious theory because it can identify the mentalistic conceptselective attention with the materialistic conceptspatial position.     

The influence of perceptual and motor factors on bimanual coordination in a polyrhythmic tapping task

Summary In this study the role of perceptual and motor factors on the motor organization (integrated versus parallel) adopted by musically skilled and unskilled subjects in a polyrhythmic tapping task was investigated. Subjects tapped a 3:2 polyrhythm to match the timing of two isochronous tone trains, one tone train for each hand. Perceptual factors were examined by the manipulation of the frequency difference between the tone trains to produce either an integrated or a streamed percept. Motor factors were examined by comparison of performance on two versions of the 3:2 polyrhythm. In one (simultaneous) version, each cycle of the polyrhythm began with a simultaneous left- and right-hand tap. In the other (shifted) version a 100-ms interval was introduced between the initial left and right taps in each cycle. Examination of the pattern of variances and covariances among intertap intervals suggested that most of the subjects in this study adopted an integrated motor organization that involved interleaving the timing of the two hands. Further analysis revealed that a serial chained model described the pattern of covariances best for the simultaneous pattern, whereas a hierarchical organization described the pattern of covariances for the shifted pattern best. The finding that performance was more accurate with integrated tones than with streamed tones provides some support for a perceptual-motor facilitation hypothesis.     

Correction processes in early reaching: Reaches by infants to prismatically displaced targets

Summary A comparison was made between trajectories of reaches to visual targets by 6-months-old infants, with and without lateral prismatic displacement. In the No Prism condition, the major element of the movement veered towards the target, confirming the results of Mathew and Cook (1990). In the Prism condition, the prism did not affect hand position or movement direction at the beginning of the major element, but a lateral displacement was evident by the end of the element. This is taken as evidence that shifts in trajectory during the element were not due to visual guidance. It is suggested instead that these shifts may reflect correction based upon somatic feedback about position in relation to the visually specified goal of the movement. Evidence that the hand approached the virtual target supports the suggestion that any visual guidance was confined to the approach phase of the reach. Nevertheless, it appears that visual guidance was operating at this stage, since movement direction was displaced away from the virtual target and towards the real target.     

A stochastic model for inter-keypress times in a typing task

A mathematical model for the inter-keypress times (IKT) in a typing task is proposed. The model, which includes a diffusion process terminated by a single response threshold, was evaluated using data obtained from typists. The differences in performance for successive cross-hand and within-hand keypresses were examined using IKT distributions and hazard functions, and it was shown that the empirical hazard functions could be fit by the theoretical hazard function derived from the convolution of normal and inverse Gaussian random variables. Some possible applications of the model for the evaluation of fatigue and strategic effects in typing are suggested.     

Interference with visual short-term memory

Working memory (Baddeley and Hitch 1974) incorporates the notion of a visuo-spatial sketch pad; a mechanism thought to be specialized for short-term storage of visuo-spatial material. However, the nature and characteristics of this hypothesized mechanism are as yet unclear. Two experiments are reported which examined selective interference in short-term visual memory. Experiment 1 contrasted recognition memory span for visual matrix patterns with that for visually presented letter sequences. These two span tasks were combined with concurrent arithmetic or a concurrent task which involved manipulation of visuo-spatial material. Results suggested that although there was a small, significant disruption by concurrent arithmetic of span for the matrix patterns, there was a substantially larger disruption of the letter span task. The converse was true for the secondary visuo-spatial task. Experiment 2 combined the span tasks with two established tasks developed by Brooks (1967). Span for matrix patterns was disrupted by a visuo-spatial task but not by a secondary verbal task. The converse was true for letter span. These results suggest that the impairment in short-term visual memory resulting from secondary arithmetic reflects a small general processing load, but that the selective interference due to mode of processing is by far the stronger effect. Results are interpreted as being entirely consistent with the notion of a specialized visuo-spatial mechanism in working memory.     

Selective response activation can begin before stimulus recognition is complete: a psychophysiological and error analysis of continuous flow

In discussions of process models of human information processing, the continuous flow conception (Eriksen and Schultz 1979) plays a prominent role. A central prediction of this conception is that any information in a display associated with a response activates that response as soon as it becomes available in the perceptual system. If it concerns the correct response channel, then response facilitation occurs. If it concerns the incorrect response channel, then response competition occurs. To assess these mechanisms more directly, we used psychophysiological measures as well as reaction time (RT). We used the latency of the P3 component of the event related brain potential (ERP) as an index of stimulus evaluation duration, the onset of lateralized motor activity derived from the ERP as an index of selective central motor activation, and the onset of electromyographic activity as an index of the start of peripheral motor activation. Subjects were required to respond to target letters that were either flanked by letters that signalled the opposite response (incompatible arrays), by the target itself (compatible arrays), by letters not associated with a response (neutral arrays), or by no other letters (targets alone). Our results replicated the basic findings obtained in this paradigm. RTs to targets alone did not differ from RTs to compatible arrays. The latter were faster than RTs to neutral arrays, which were faster than RTs to incompatible arrays. P3 latencies were longer on incompatible than on neutral trials, and longer on compatible than on target alone trials. Incorrect central response activation on incompatible trials and correct central response activation on compatible trials, both began earlier than on target alone trials. Peripheral responding on both trial types, however, began later than on target alone trials. More incompatible but less compatible trials than neutral ones exhibited incorrect peripheral response activation. Peripheral response execution was faster and more accurate on compatible than on target alone trials, while it was slower and less accurate on incompatible than on neutral trials. These results indicate, that the flankers activated their associated response channel while display evaluation was still going on, and that response facilitation and competition occurred. After applying criteria proposed by Miller (1988), it was concluded that the set of stimulus recognition processes and the set of response activation processes cannot be regarded as independent stages of processing.     

Identification of letters in the predesignated target paradigm: a word superiority effect for the common word the

The size of the perceptual unit used in reading was addressed using the predesignated target paradigm. Sixteen subjects viewed the following stimuli in random order: the words tee, the, tie, and toe; the nonwords eet, eht, eit, and eot; and the letters e, h, i, and o. Subjects fixated on the location of the center letter and identified the letter as e, h, i, or o, alternatives which were known to them at the onset. A word superiority effect was obtained for the common word the but not for the less common words tee, tie, and toe. The word superiority effect was attributable to bias rather than discriminability: Subjects exhibited a bias to perceive the words in this experiment as the (i.e., there was a bias to perceive h in the t e stimulus presentations). These results suggest that the common word the is processed in reading units that are larger than the letter, and that the system is biased to perceive common rather than uncommon words in data-limited conditions.     

The relationship of appraisal and coping to chronic illness adjustment

There is evidence that adaptation to chronic illness may be affected by psychological factors, especially how patients appraise and cope with the stress of their illness. The purpose of the present study was to examine the relationship of stress appraisal and coping responses to multiple behavioral indices of illness adjustment among patients with diverse chronic medical conditions. One hundred and one patients admitted to a multidisciplinary medicine/psychiatry unit completed measures of functional impairment, depression, symptom severity, and the Ways of Coping Checklist--Revised. Hierarchical regression analyses indicated that emotion-focused coping was positively related to poor psychosocial adjustment and depression after controlling for physician rated disease severity. Appraising chronic illness as holding one back predicted greater emotion-focused coping responses and poorer adjustment to illness. The use of problem-focused coping strategies was generally unrelated to illness adjustment. These findings suggest the presence of an emotion-focused coping triad consisting of wishful thinking, self blame, and avoidance, all of which appear to be maladaptive strategies when coping with chronic medical conditions. Implications for coping skills training and the need for longitudinal research is discussed.     

Pessimistic explanatory style and response to illness

Previous studies have shown that a pessimistic explanatory style is a risk factor for illness, but the factors linking explanatory style and illness are unknown. One's characteristic response to poor health may mediate this relationship. Perhaps pessimistic individuals act helplessly in the face of their symptoms, thereby exacerbating disease. In the present study, we investigated this possibility by asking 96 young adults to complete measures of explanatory style, habitual response to illness, and ways of coping during their most recent episode of illness. Subjects who explain bad events pessimistically (with internal, stable, and global causes) reported more frequent illnesses during the past year and rated their overall health more poorly than those who habitually favor external, unstable, and specific explanations. When ill, the pessimistic subjects were less likely than their optimistic counterparts to take active steps to combat their illness. Our results suggest that one pathway leading from pessimistic explanatory style to poor health is mundane: passivity in the face of disease.