Capacity limitations in visual word processing

The ability of subjects to process English words in a spatially parallel manner was examined in several redundant-target detection tasks. When redundant targets were identical in a given display, processing limitations were evident in a task that required subjects to make semantic categorizations of words. However, parallel processing of identical redundant target words was exhibited in a lexical decision task that required a structural analysis of letter strings, but not an analysis of word meaning. The difference in performance in the two tasks suggests that the capacity for semantic processing is limited. Analyses designed to examine whether the redundancy gain in Experiment 2 could be attributed to limited capacity processing in conjunction with positional preferences provided evidence against this possibility. In addition, these analyses suggested that the processing times for the redundant targets in Experiment 2 might be positively correlated. In the third and fourth experiments, the redundant-target displays contained two different words. Processing interference, in the form of a redundancy loss, was evident in the lexical decision task, but not in the semantic categorization task, confirming a difference in the mode of processing between the two tasks. The results provide evidence against the unlimited-capacity, parallel processing hypothesis of late selection theories of attention.     

Independence versus interference in the perceptual processing of letters

Several experiments are reported that help resolve the discrepancy between studies indicating that letters are perceived independently and studies showing perceptual interference between letters. Two variables were examined which, based on the existing literature, appeared to be important in distinguishing between the perceptual independence and perceptual interference studies. In Experiment 1, the amount of spatial separation between letters was varied. Surprisingly, the letters were perceived independently, regardless of the amount of separation or degree of similarity between them. Thus, it was concluded that the amount of interletter separation is not sufficient to account for the difference between studies demonstrating independence and those demonstrating interference. The results of Experiments 2 and 3 indicated that the type of perceptual limitation that is used to control response accuracy determines whether perceptual independence or interference is obtained. Specifically, perceptual interference was obtained only under masking conditions, whereas perceptual independence was obtained only under energy-limited (no-mask) conditions. Experiment 4 extended these results, indicating that perceptual interference is obtained under prestimulus as well as poststimulus masking conditions. Several interpretations of the perceptual interference data are considered, and it is concluded that the data can best be accounted for in terms of a model based on the principle of feature-specific inhibition.     

Cognitive correlates of map-reading ability

The performance of ROTC students on the Relief Format Assessment Test (RFAT) was regressed on psychometric variables and a measure of hemisphericity. Contrary to expectation, it was found that measures of visual-spatial ability and hemisphericity were not good predictors of map-reading ability, whereas the Extended Range Vocabulary and Mathematical Aptitude Tests were significant predictors. Factor analysis of the RFAT indicated the existence of two factors, one tentatively associated with terrain analysis and the other with altitude estimation. Mathematical Aptitude along with Form Board predicted performance on the altitude estimation factor, whereas Extended Range Vocabulary along with Similarities and Institution predicted performance on the terrain analysis factor. These results suggest that at least for our subjects, the solution of map-reading problems is primarily dependent upon verbal-analytic and to a lesser extent upon visual-spatial ability.     

Interference in letter identification: A test of feature-specific inhibition

The role of perceptual interference in letter identification was investigated in three experiments designed to test the feature-specific inhibition model proposed by Bjork and Murray (1977). According to their extension of Estes’ (1972, 1974) interactive channels model, input channels leading to the same feature detector inhibit one another more than do channels leading to different detectors. The model therefore predicts perceptual interference between two letters to be a function of the degree of their feature overlap. Experiment 1 confirmed the feature-specific inhibition model and Bjork and Murray’s finding that the accuracy of report is lower when a briefly presented target letter is flanked by an identical letter than when flanked by another target letter or by a nontarget letter. Results from Experiment 2 indicated that single-target performance is a function of the degree of feature similarity between the target letter and background characters in a stimulus display. Experiment 3 ruled out a spatial-uncertainty explanation of feature-specific inhibition in a new paradigm that does not require subjects to process a poststimulus cue. The results of these experiments are discussed in relation to recent studies exhibiting strong effects of noise letters at the response stage of processing. It is suggested that discrepancies between feature-specific interference and response-interference studies may be a function of the particular mode of stimulus presentation and of the dependent measures that are used.     

Multidimensional stimulus identification

In an absolute judgment task, total information transmitted about a set of stimuli increases as the dimensionality of the stimuli is increased. However, as the number of dimensions is increased, information transmitted about each component dimension decreases. Four factors were proposed that might, singly or in combination, account for this decrement: stimulus duration, interdimensional interference, distraction, and response complexity. The results of four experiments established that each of these factors may be operative under appropriate circumstances. It was also concluded that component dimensions were processed simultaneously rather than sequentially. However, the processing was not truly parallel because the input channels were not independent of one another.     

Differential effects of familiarity on judgments of sameness and difference

Ss indicated whether pairs of simultaneously presented objects were “same” or “different.” In Experiments 1, 2, and 3 the stimuli were pairs of letters, and familiarity was manipulated by showing the letters in either an upright or an upside-down orientation. In Experiments 4 and 5 the stimuli were pairs of trigrams, and familiarity was manipulated either by rotation or by selection according to rated meaningfulness. Analysis of reaction times indicated that familiar pairs were responded to more quickly than were unfamiliar pairs; however, this was true only for “same” judgments, not for “different” judgments. In addition, Experiment 3 indicated that familiarity influenced discrimination accuracy under conditions of tachistoscopic exposure. Finally, in Experiment 6 an effort was made to disentangle the effects of meaningfulness from the effects of pronounceability. The present results stand in contrast to previous research using perceptual comparison tasks, since the earlier work failed to indicate any effect of familiarity.     

Detecting conjunctions of color and form in parallel

Researchers have proposed that graphical efficacy may be determined, in part, by the nature of the perceptual interactions that exist between attributes used to create graphical displays. One extreme type of interaction isintegrality, in which two or more physical dimensions are represented as a single psychological dimension in the observer. An alternative type of interaction isconfigurality, in which a global emergent dimension is availableto the observer in addition to the component attributes. Thirteen stimulus sets, each composed of attributes commonly used in the design of graphs, were submitted to the performance-based diagnostics of integrality and configurality. Analyses suggest a continuum of configurality among the present stimulus sets, with little evidence for integral graphical attributes. The configural pattern of results was more common when two identical dimensions were paired (homogeneous stimuli) than when two different dimensions were paired (heterogeneous stimuli). However, there was no evidence that pairs of dimensions belonging to a single object (object integration) were any more configural than dimensions belonging to different objects. Object integration was, however, consistently related to inefficient performance in tasks requiring the filtering of one of two component dimensions.