The properties of serial position functions for tachistoscopic report were investigated over a wide ra!J.ge of viewing times. Four-letter strings of random consonants were presented in varying display loc~ions relative to the fixation point with the observers' eye movements monitored to limit them to a single fixgtion for each display. Salient properties of the serial position curves include an overall central-peripheral gradient, higher performance at the ends than the interior of letter strings regardless of absolute location, and left-right asymmetry in the visual field, all of these being largely independent of viewing time. Errors reflecting loss of positional information are prominent even at extended viewing times, are more nearly symmetrical in the left and right visual fields than other types of errors, and, in contrast to item errors, occur less frequently in letter sequences that have high frequencies in English. Further, transposition errors exhibit a pronounced peripheral-to-central drift, possibly reflecting gradients of positional uncertainty. Such gradients may be implicated in the peripheral-central asymmetry of the lateral interference effects exerted by other letters on a target letter in a nonfoveallocation.

The ability to detect simple types of visual information from various locations in the visual field was examined in two experiments. In both, the four locations containing the information to be detected were presented either simultaneously or sequentially, with the presentation time per location identical for both conditions. Limitations of capacity and attentional control of perceptual processing would predict sequential presentation to be superior to simultaneous presentation, since, in the former case, attention need not be shared among four locations. The results showed equal detection performance for both conditions. Thus, spatial attention was not present during detection of horizontal and vertical dot pairs (Experiment I). 0 differences (probably due to strategies) make the same conclusion more difficult to draw for single-dot detection (Experiment II). Similar findings and conclusions were reported by Shiffrin and Gardner (1972) in studies utilizing alphabetic characters.SENSORY PROCESSING MODELS perceptual processing. All attentional effects are due to characteristics of short-term store following perceptual processing. Deutsch and Deutsch (1963) and Deutsch, Deutsch, and Lindsay (1967) have proposed such a model for auditory processing. Gardner (1970Gardner ( , 1973, Shiffrin and Gardner (1972), and Shiffrin and Geisler (in press) have proposed this model for visual processing and general sensory processing; Shiffrin, Craig, and Cohen (in press) proposed such a model for tactile processing.The Shiffrin and Gardner (1972) result is particularly important because it places clear and severely limited bounds on the degree of attention which is present in visual processing. Their result argued strongly for a model of the nonattention type, the lower model in Fig. 1. The paradigm was based in part upon an earlier one by Eriksen and Spencer (1969) and tests the ability The questions of attentional control and limitations of capacity in sensory information processing are among the most basic in psychology. Figure 1 presents three of the commonly proposed models of sensory processing. The top panel illustrates a single-channel model in which information enters the system from only a single source at anyone moment. It is assumed in this model that attention is switched rapidly among various possible sources of sensory information. Models similar to this were originally proposed by Broadbent (1958) in the context of dichotic listening experiments. Franzen, Markowitz, and Swets (1970) proposed a model of this type for the processing of near-threshold vibrotactile information. Taylor (1964, 1966) proposed a model of this type for visual processing. A less extreme attentional model is shown in the middle panel of the figure. In this attenuation model, total processing capacity is limited, but some input is simultaneously or serially processed from many channels. The O's attentional control determines the amount of information processed in particular channels. Treisman (1969), Moray (1970), and Neisser (1967 have p...

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