Contrasting effects of sensory limits and capacity limits in visual selective attention

The effects of perceptual load and those of target-stimulus degradation on distractor processing were contrasted. Targets either had to be found among several nontargets (high perceptual load) or were presented alone and were intact (low perceptual load), had reduced size and contrast (Experiment 1), had reduced duration and were followed by a mask (Experiment 2), or had reduced visual acuity owing to position eccentricity (Experiment 3) in the degraded low-load condition. The results showed that both high perceptual load and target degradation increased general task difficulty, as is reflected by overall reaction times and accuracy. However, whereas high perceptual load reduced response-competition effects of irrelevant distractors, target degradation increased distractor effects. These results support the hypothesis that distractor processing depends on the extent to which high perceptual load exhausts attention in relevant processing and provide a dissociation between perceptual load and general task difficulty and processing speed.     

Sex in lateralized tachistoscopic word recognition

Although a generalized sex difference in lateralization appears to be established, a review of the literature pertaining to lexical tachistoscopic tasks suggests a dissociation by method: females show reduced visual field asymmetries relative to males in lexical decision and naming, but not in word recognition. Here 14 recognition experiments from the author's laboratory are subjected to meta-analysis, and the literature review is confirmed. There is no sex difference is visual field asymmetry for the task, although an overall field difference is found and statistical power is high to find the interaction. Possible reasons for the discrepancy with lexical decision and naming findings are discussed. One possibility is that stress on reaction time in those tasks produces a complex interaction between sex, activation/arousal, and hemispheric differences, which is not found when a less speeded method is used.     

Cross modality facilitation in tachistoscopic word recognition

In its old form, the logogen model (Morton, 1969) would have predicted extensive cross-model facilitation of tachistoscopic word recognition. An experiment by Winnick and Daniel (1970) violated this prediction by showing no effects on subsequent visual word recognition of naming a picture or filling a definition. The latter results was replicated, and it was also found that pretraining with handwritten words transferred to printed words from 10-45 min later. A further experiment showed no significant transfer from auditory presentation to subsequent visual recognition. A third experiment, designed to minimize the role of conscious guessing strategies showed a significant cross-model transfer. The logogen model was modified substantially in the light of these data. There are now seen to be modality specific input categorization systems which are separate from the output lexicon and which are identified as the site of facilitation in the experiments.     

Order of report and processing in tachistoscopic recognition

Two groups of 12 Ss were shown tachistoscopically 4 letters and 4 numbers. Within these alpha-numeric sequences, three variables were systematically manipulated: grouping of items, initial item, and familiarity of the letter sequences. One group of Ss reported first letters then numbers from each sequence; the other group reported numbers then letters. The results indicated that grouping, redundancy, and order of report had significant effects on letter accuracy but not on number accuracy. These effects were interpreted in terms of processing, particularly the use of spatial and identity information during recognition.     

Some factors affecting tachistoscopic letter recognition

Summary The paper reports a series of studies that attempt to examine the issue of tachistoscopic identification of letter material. In particular a reductionist approach is used to investigate the influence of retinal locus, cerebral dominance, metacontrast, letter symmetry, and ocular dominance on the task. Retinal locus, metacontrast, and ocular dominance were shown to influence letter reportability under the present conditions with, it is argued, retinal locus and metacontrast affecting the integrity of the icon. Evidence is given for the construct of ocular dominance as the eye (dominant) initiating eye movements with the other passively following.     

Buffer storage modality and identification time in tachistoscopic recognition

According to Sperling's (1967) model of short-term memory briefly presented masked stimuli are rapidly read into a non-visual Recognition Buffer (the RB model). An alternative interpretation of the data is that the stimulus information is coded into a non-iconic Visual Buffer where it is held while a much slower recognition process takes place (the VB model). The high frequency of errors in experiments with sequentially presented stimuli appears to refute the possibility that recognition is as rapid as suggested by the RB model. However these data may be attributed to variations in effective stimulus duration and stimulus quality rather than to slow recognition time. In an experiment to control for these effects, normal, laterally inverted and spaced digits were presented in a rapid sequence (1-10 items/s) with intervening pattern masks to keep the stimulus/mask interval constant. The recall data showed that order errors increased with rate of presentation but that item errors remained invariant. At the fastest rates of presentation there were fewer order errors for spaced than for coincident digits. It was argued that the results, as a whole, were more consistent with the VB than the RB model and that there is no evidence for identification times as fast as 10-40 ms/item.     

Disruptive effects of prior information on tachistoscopic recognition

Smith, Haviland, Reder, Brownell, and Adams (1976) found tachistoscopic letter recognition to be disrupted by advance information about possible letter alternatives. An association of “before-disruption” with a bias to respond “same” in same-different judgment led Smith et al. to conclude that incidental mask features corresponding to a precued letter were erroneously incorporated into the target letter decision. Experiments 1 and 2 in the present study failed to replicate the before-disruption effect under conditions similar to those of Smith et al., although precuing produced a strong bias to respond “same.” Similarity between “same” and “different” alternatives was manipulated in Experiment 3 by selecting letter pairs differing in one critical feature (P-R, O-Q, C-G, F-E) for one group of subjects, and re-pairing the same letters (P-G, O-E, C-R, F-Q) for another group. Contrary to Smith et el., precuing interacted significantly with pair similarity, such that before-disruption occurred only with similar alternatives. In contrast, precuing produced equivalent “same-bias” in both groups. The dependence of before-disruption on pair similarity was extended to two-alternative forced-choice recognition in Experiment 4. Together with inconsistencies in the Smith et al. data and more detailed analysis of present recognition errors, the results suggest (1) the before-disruption and same-bias effects of precuing are mediated by separate mechanisms, and (2) before-disruption reflects loss of target letter information rather than direct incorporation of extraneous mask features.     

The role of neuromodulators in selective attention

Several classes of neurotransmitters exert modulatory effects on a broad and diverse population of neurons throughout the brain. Some of these neuromodulators, especially acetylcholine and dopamine, have long been implicated in the neural control of selective attention. We review recent evidence and evolving ideas about the importance of these neuromodulatory systems in attention, particularly visual selective attention. We conclude that, although our understanding of their role in the neural circuitry of selective attention remains rudimentary, recent research has begun to suggest unique contributions of neuromodulators to different forms of attention, such as bottom-up and top-down attention.     

The limits of top-down control of visual attention

The extent to which spatial selection is driven by the goals of the observer and by the properties of the environment is one of the major issues in the field of visual attention. Here we review recent experimental evidence from behavioral and eye movement studies suggesting that top-down control has temporal and spatial limits. More specifically, we argue that the first feedforward sweep of information is bottom-up, and that top-down control can influence selection only after the sweep is completed. In addition, top-down control can limit spatial selection through adjusting the size of attentional window, an area of visual space which receives priority in information sampling. Finally, we discuss the evidence found using brain imaging techniques for top-down control in an attempt to reconcile it with behavioral findings. We conclude by discussing theoretical implications of these results for the current models of visual selection.