Identification, localization, and “iconic memory”: An evaluation of the bar-probe task

Abstract

The partial report tachistoscopic task has been used to define "iconic memory," a labile image-like precategorical visual store. Six interrelated partial report studies are reported that challenge the construct. On each trial, subjects were shown an eight-letter pseudoword (representing one of four orders of approximation to English) and a bar probe indicating which letter to report. The probe was delayed systematically, and the experiments included both mask and no-mask conditions. All three variables-familiarity of the material, masking, and delay of the probe-affected accuracy of report. Delaying the probe, for example, reduced accuracy by increasing location errors. Delaying the mask increased accuracy by reducing both location and item errors, but it did not reduce the location errors until its effect on item errors had reached asymptote. Across the stimulus array, however, masking reduced accuracy at all delays by increasing location errors. Finally, the greater accuracy associated with higher orders of approximation to English was complemented by a decrease in item errors, but the familiarity factor had no effect on location errors. Taken together, even though the task has been used to define the idea, the results indicate that the bar-probe task cannot be explained in terms of a simple iconic memory concept. Instead of a simple image-like buffer, the explanation requires , a feature buffer, an "intelligent" letter identification process, and a postidentification character buffer. Iconic memory is a construct that oversimplifies the information processing system used in the bar-probe task.

Sensory registration and informational persistence.

“…Each of these responses was scored as either a correct report (if the correct letter was reported in the correct position), a location error (if a letter from the 3X3 stimulus display was reported, but in the incorrect position), or an intrusion error (if a letter not contained in the 3 X 3 stimulus display was reported). Although this classification of the responses is straightforward, Mewhort et al (1981) have pointed out that interpretation of their underlying causes is not; correct reports are a fairly unambiguous indicator of accuracy, and intrusion errors of misidentification, but location errors may be due to either localization failure or misidentification. Thus, intrusion and location errors are only imperfect indicators of misidentifications cue delay (0, 50, 150, 300, 500 ms).…”

“…Both sources of information might decay rapidly in this memory, with faster decay for the spatial coordinates. Several models of this type have recently been proposed (e.g., Coltheart, 1980Coltheart, , 1984Di Lollo, 1978Mewhort et al, 1981Mewhort et al, , 1984; although these models differ in various ways, what they all share in common is the assumption that persisting information is recoded into a postcategorical, nonvisual format as time elapses from stimulus onset, and that it is this nonvisual information that is accessed by the partial report technique. The particular model of nonvisual informational persistence that we tested is that of Di Lollo, because it makes clear and specific predictions about subjects' performance in the experimental task that we employed.…”

Spatiotemporal Segregation in Visual Search: Evidence From Parietal Lesions.

“…At longer intervals (between 100 and 200 ms), so-called location errors become relatively more frequent: Observers report an item that was present in the display but at a different position than the cued one, with positions near the cue being preferred (see also Eriksen & Rohrbaugh, 1970;Snyder, 1972;Townsend, 1973). Mewhort et al (1981) interpreted this pattern as evidence that, with increasing stimulus-cue intervals, spatial information from the array is lost, whereas identity information is preserved. Although attention was never explicitly manipulated in these studies, one may infer from the volatility of spatial representations relative to identity representations that because the attentional blink affects the latter, it must certainly also affect the first.…”

The CODE theory of visual attention: An integration of space-based and object-based attention.

“…The key to fitting these data may lie in a proximity effect reported by Snyder (1972) and Mewhort, Campbell, Marchetti, and Campbell ( 1981 ). In partial report tasks that probe for a single item rather than a set of items, errors are often correct reports of the letters adjacent to the target item.…”

“…Adjacent items are more likely than nonadjacent items to intrude in the target's feature catch because the feature distribution falls off exponentially as distance increases. Thus, in principle, CTVA can account for the Snyder (1972) and Mewhort et al ( 1981 ) results. The question is whether it can account for them quantitatively, using reasonable parameter values.…”