Search

In the present study, we investigated whether judging the presence of multiple features within an object would be superior to judging the presence of only one feature. Feature discriminability and the number of features to discriminate within an object were varied. Specific features were judged as present or absent. Results showed that judging the presence of two or three features was faster than judging the presence of the less discriminable of these two or three features alone (multiple-feature benefits). These findings suggest that relevant features within an object activate (prime) a decision or response in a parallel, asynchronous fashion based on discriminability (Miller, 1982a). The ability of a response priming model, a response mapping model, and a template model to account for multiple-feature benefits is discussed.

Judgments of same and different on a comparison task have been found to be subject to response competition if an irrelevant stimulus is presented in the display along with the target stimuli. For example, the reaction time for judging two letters the same is markedly increased if a different but irrelevant letter is also present in the display (C. W. Eriksen, O'Hara, & B. [A.] Eriksen, 1982). We have made use of this competition effect to map the visual attentional field in two dimensions. In two experiments, we varied the size of the attended area by varying the separation of the comparison stimuli. The boundaries of the attended area were mapped by varying the location of a response-competitive irrelevant noise letter. On this task, the attended area was found to be elliptical in shape, with the location of the target stimuli defining the major axis. The minor axis of the ellipse increased in direct proportion to increases in the major axis. Rather than interpret these field effects in terms of areas of enhanced processing, we propose that instead they represent the limits or failures in inhibition of competing stimulation.

An experiment of McLean, D. E. Broadbent, and M. H. P. Broadbent (1983) using rapid serial visual presentation (RSVP) was replicated. A series of letters in one of 5 colors was presented, and the subject was asked to identify the letter that appeared in a designated color. There were several innovations in our procedure, the most important of which was the use of a response menu. After each trial, the subject was presented with 7 candidate letters from which to choose his/her response. In three experimental conditions, the target, the letter following the target, and all letters other than the target were, respectively, eliminated from the menu. In other conditions, the stimulus list was manipulated by repeating items in the series, repeating the color of successive items, or even eliminating the target color. By means of these manipulations, we were able to determine more precisely the information that subjects had obtained from the presentation of the stimulus series. Although we replicated the results of McLean et al. (1983), the more extensive information that our procedure produced was incompatible with the serial filter model that McLean et al. had used to describe their data. Overall, our results were more compatible with a parallel-processing account. Furthermore, intrusion errors are apparently not only a perceptual phenomenon but a memory problem as well.

The early versus late selection issue in attention models was examined by means of a new methodology. Through cues or precues, attention was directed to one location of a multistimulus visual display and, while attention was so engaged, the identity of a stimulus located at a different position in the display was changed. By varying the time after display onset before the stimulus was changed, we controlled the preview time that the original stimulus was represented on the retina. Then, using a marker cue, we directed the subject's attention to the location of the changed stimulus. The subject's response was a timed discrimination between two possible target letters. The data of main interest was the effect of preview time upon the subject's latency in identifying the new target that appeared in the changed location. We found that the preview time of the original stimulus, before RT was affected to the new target, depended upon whether the original stimulus was a neutral (noise) letter or whether it was the alternative target. When the original stimulus was a noise letter, RTs to the new target were just as fast as those obtained in the control condition in which the target was present throughout the preview interval and did not change its identity. Significant effects upon RT were obtained at preview times of 83 msec when the original stimulus was one of the targets that changed to the alternative target. Preview times also varied as a function of precuing. Preview times were correspondingly shortened when the first cue occurred 50 msec before display onset, thus providing an extra 50 msec for attention to be directed to the first display location. The results were interpreted in terms of two separate information-processing systems in the human: an automatic system and an attentional system. Even though a stimulus may have been automatically processed, when the attention system is directed to that stimulus, processing starts at the beginning again.

If several positions must be attended in a large visual display, does the efficiency of performance vary as a function of the display distance between these to-be-attended positions? Two previous experiments (Podgorny & Shepard, 1983; Shaw, 1978) gave conflicting answers. In the present experiments, eight-letter circular displays were briefly presented. On each trial one, two, or three positions of the display were cued or precued. The number of noncued display positions intervening between the cued locations varied from zero to three. The subjects' task was to rapidly discriminate between two target letters. Although reaction time was found to increase with increases in the number of cued locations, no significant or suggestive effects were found for the spacing or distance between the cued locations. The evidence strongly suggests that the subjects serially searched the cued locations, which further implies that attention can index locations in the visual field at a speed that is independent of the distance between these locations.

The evidence for and against a redundancy gain in reaction time (RT) when the target is repeated in the visual display is reviewed. We consider the relevance of redundancy gains under these circumstances to the question of whether attention can be simultaneously directed to separate locations in the visual field. In the present experiments, two capital letters were the target stimuli in a two-alternative forced-choice RT paradigm. In addition to the usual conditions of single-target trials, trials on which the target is repeated in the display, and trials on which the target occurs with a noise letter, we introduced the innovation of a condition in which both targets occur in the display. In our two experiments, RT was fastest with single-target displays and slowest with displays containing a target and a noise letter. There was no significant difference in RT to displays in which the target was repeated and displays in which both targets were presented. Both conditions showed a redundancy gain when compared with displays containing a target and a noise letter. The lack of response competition in the both-targets condition and the overall pattern of the results were well explained by a unitary attentional focus that serially processed the letters in the display. Analyses of minima and maxima RTs were consistent with this interpretation.