Early and late selection in partial report: Evidence from degraded displays

Abstract

In studies of iconic memory using the bar-probe task, subjects see a brief display of target letters and are probed by an arrow to report one of them. According to the classic early-selection account, subjects use the probe to select material for perceptual analysis from a precategorical (iconic) memory, but according to late-selection theories, subjects first identify the letters and then use the probe to select one letter for report from the set of categorized items. Pashler (1984) based his test for the locus of selection on a manipulation of display quality in previewed displays. He presented a target for 200 msec and then added a probe, together with the target, for an additional 150 msec. Reducing the target's stimulus quality increased response latency. If the subjects identified the characters before the probe appeared and then selected an item for report, the clarity of the original array should not have affected response latency. Hence, Pashler concluded that his subjects used the probe to select from a precategorical store (early selection). Pashler's experiment did not force subjects to rely on memory of the target; hence, although his experiment documented a situation in which subjects used early selection, it did not rule out late selection in studies of information persistence. We replicated Pashler's findings and, using his logic, showed that when subjects are forced to rely on memory of the target, they select from a categorized store.

Awareness of the continuously visible: Information acquisition during preview

“…This finding held true even when unpredictable catch trials were introduced in which the display was masked immediately after preview, in order to give subjects every incentive to process the display as extensively as possible during the preview. Mewhort, Johns, and Coble (1991) confirmed this basic result (persistence of the degradation effect after preview), using a different manipulation of degradation: dots superimposed on top of characters.…”

“…On half the trials, the letters were visually degraded, much as in Mewhort et al (1991). The subjects' task was to determine whether a target letter (which varied from trial to trial) was present in the display.…”

“…To test the generalizability of this model, we sought to apply it to another set of data derived from a visual quality manipulation that is more typical of visual quality manipulations in the literature. Several researchers who have examined visual quality effects in search have found these effects to be additive with display set size (Egeth & Dagenbach, 1991;Logan, 1978;Mewhort et al, 1991;Pashler & Badgio, 1985). These authors generally concluded that degrading the visual quality of a display affects only the sensory encoding stage of the search task and that encoding can be done in parallel across the visual field.…”

Negative priming depends on ease of selection

“…There was also a significant main effect of SOA [F(6,174) = 2.47, p < .05]; the subjects responded slightly faster to probe displays following color-first prime displays. vant before fully identifying perceptually degraded letters in a bar-probe task (Mewhort, Johns, & Coble, 1991;Pashler, 1984). Note that the strategy of preventing the identification of stimulus letters that are not known to be relevant is perfectly consistent with the notion of selective identification.…”

Evidence against early selection: Stimulus quality effects in previewed displays.

“…However, weaker late selection theories that produce either location or identity information could accommodate Pashler's pattern of results. Mewhort et al (1991) extended Pashler's (1984) work by examining the effects of degraded displays in partial report. In Experiment 1 of their article, they described a successful replication of Pashler's study, demonstrating that effects of stimulus degradation were not reduced when subjects received a preview of the display array.…”