Flanking Letters Research Articles

The flanker compatibility effect as a function of visual angle, attentional focus, visual transients, and perceptual load: A search for boundary conditions

When subjects must respond to a relevant center letter and ignore irrelevant flanking letters, the identities of the flankers produce a response compatibility effect, indicating that they are processed semantically at least to some extent. Because this effect decreases as the separation between target and flankers increases, the effect appears to result from imperfect early selection (attenuation). In the present experiments, several features of the focused attention paradigm were examined, in order to determine whether they might produce the flanker compatibility effect by interfering with the operation of an early selective mechanism. Specifically, the effect might be produced because the paradigm requires subjects to (1) attend exclusively to stimuli within a very small visual angle, (2) maintain a long-term attentional focus on a constant display location, (3) focus attention on an empty display location, (4) exclude onset-transient flankers from semantic processing, or (5) ignore some of the few stimuli in an impoverished visual field. The results indicate that none of these task features is required for semantic processing of unattended stimuli to occur. In fact, visual angle is the only one of the task features that clearly has a strong influence on the size of the flanker compatibility effect. The invariance of the flanker compatibility effect across these conditions suggests that the mechanism for early selection rarely, if ever, completely excludes unattended stimuli from semantic analysis. In addition, it shows that selective mechanisms are relatively insensitive to several factors that might be expected to influence them, thereby supporting the view that spatial separation has a special status for visual selective attention.

Evidence for early selection: Precuing target location reduces interference from same-category distractors

In this study, we evaluated whether uncertainty about target location and category overlap between the target and the flankers played a role in recent findings (Miller, 1987) of semantic interference of irrelevant stimuli. In each of four testing conditions, subjects were required to identify a target letter surrounded by irrelevant flankers whose identity predicted the correct response. We varied (1) whether or not the target location was precued, and (2) the flanker's category (digits vs. letters). We found a substantial effect of letter flankers when subjects were uncertain of the precise target location. However, this effect was greatly attenuated when attention was predirected to the target location. Similarly, a reduced flanker effect was observed when the flankers (digits) belonged to a different semantic category than the target. However, when the target location was precued, no effect of the semantic congruity of target and flankers was found. Coupled with previous research, these findings converge in establishing that both failures to maintain attention on the target location and the semantic congruity of target and flankers modulate the size of the effects from irrelevant stimuli. These results are discussed in the context of early and late selection views of selective attention.

Effect of familiarity and category contrast on stimulus and response priming.

In a letter-symbol classification task, flanking incompatible symbols slowed response latencies to letter targets, whereas incompatible letter flankers did not slow the classification of symbol targets. The conditions surrounding this asymmetry in response competition were investigated in five experiments. The results showed that: (1) the asymmetry was not related to the familiarity of the symbol targets or to the prime-target interval; (2) when the classification involved familiar and unfamiliar symbols, the asymmetry remained (i.e., there was less interference associated with the unfamiliar symbol targets), but there was now significant response competition associated with both symbol categories; and (3) with a mixed-category task (i.e., letters and symbols assigned to both responses), the symbol targets continued to be less interfered with by both letter and symbol incompatible flankers. These findings were interpreted as suggesting that response competition can be influenced by both classification decision rules and cohesiveness of exemplars comprising a category.

Response-compatibility effects in focused-attention tasks: a same-hand advantage in response activation.

Previous studies have shown that responses can be partially activated by irrelevant stimuli in focused-attention tasks. In two experiments, such response activation was used to investigate the organization of keypress responses. Stimuli were rows of three letters, with a relevant target letter in the middle of the row and irrelevant flanker letters on the outside. There were four target letters, and these were assigned to four keypress responses made with the index and middle fingers of the two hands. Irrelevant flankers were parentheses, a neutral letter, or one of the four target letters. Responses were fastest when flankers were identical to the target, indicating facilitation of a response activated by both relevant and irrelevant letters. When flankers were response-incompatible target letters, responses were faster if these were target letters assigned to a response finger on the same hand as the correct response than if they were target letters assigned to a response finger on the opposite hand. The latter result is consistent with the hypothesis that simultaneous activation of two response fingers on the same hand produces faster responses than simultaneous activation of two response fingers on different hands, as assumed by Miller (1982). In Experiment 2, flankers were presented slightly before targets, and flankers that were same-hand target letters sometimes facilitated responses relative to the neutral parentheses flankers.

Priming is not necessary for selective-attention failures: semantic effects of unattended, unprimed letters.

Certain experimental effects indicate that unattended stimuli are sometimes processed semantically (e.g., B. A. Eriksen & C. W. Eriksen, 1974; Stroop, 1935). Previously, such effects have been demonstrated primarily in situations in which the identities of the unattended stimuli would have been primed by task relevance, and it is possible that such priming is necessary for unattended stimuli to be processed semantically. Six experiments examined the importance of such priming in the selective-attention paradigm of Eriksen and Eriksen. (1974). Subjects classified target letters presented in the relevant center position of a three-letter visual display, ignoring simultaneously presented irrelevant flanker letters on each side of it. Across trials, identities of the flankers were correlated with, and therefore predictive of., correct responses. Although subjects had been instructed to ignore the flankers and later seemed to have no awareness of their correlation with responses, response times indicated that subjects learned and were influenced by the predictive relationship of the flanker to the response. This effect provides an example of semantic processing of unattended stimuli that have not been primed by either task relevance or long-term relevance. It is also of interest as an example of associative learning that is both incidental and apparently unconscious.

The interfering effect of word perception on letter identification.

Subjects identified a single lowercase letter in a visual display by pressing one of two buttons. Two letters were assigned to each response. Groups received one of three context conditions: word, nonword, or single-letter displays. In words and nonwords, the flanking letters adjacent to the target varied as to whether they were response compatible or incompatible with the target. Single letters produced faster response latencies than either multi-letter condition, and words yielded slower latencies than did nonwords. Items Containing an incompatible-response flanking letter produced longer latencies than items containing a compatible flanking letter. Subgroups of subjects with different characteristic processing patterns were identified with a separate test. These subgroups were differentially affected by the context conditions in the letter-identification task. A greater subgroup difference was found in nonwords than in words.