THE STROOP EFFECT: FURTHER TESTS OF THE ATTENTION-CAPTURE HYPOTHESIS

Authors Avatar
THE STROOP EFFECT: FURTHER TESTS OF THE ATTENTION-CAPTURE HYPOTHESIS

ABSTRACT

Building on the work of Kahneman and Chajcek (1983) and MacLeod and Hodder (1998), this study examined the role of attention in the Stroop effect. A computer-controlled colour-word stimulus presentation and key-press response technique were used to study colour naming response times for dissimilar incongruent word pairs relative to identical incongruent word pairs, and response times for congruent-incongruent word pairs relative to congruent-congruent pairs and incongruent-incongruent pairs. The effect of word position was also investigated. It was found that a stimulus of two different incongruent words produced no more interference than a stimulus of two identical incongruent words and that congruent-incongruent word pairs produced more interference than congruent-congruent pairs but less than incongruent-incongruent pairs. The position of words in the pair had no significant effect. These results contradict the response competition hypothesis and provide further support for the attention-capture hypothesis of Kahneman and Chajcek (1983). However, the factors involved in allocation of attention remain unclear, and it is suggested that these be more thoroughly investigated.

INTRODUCTION

Presented with a stimulus varying on the two dimensions of word and colour, people seem incapable of ignoring the word dimension even when it is irrelevant to the task of naming the colour. This was first demonstrated by Stroop (1935): he gave subjects a list of words printed in different colour inks, and found that while incongruent colours did not interfere with word reading, incongruent words interfered significantly with naming colours, as indicated by longer response times for colour naming. This effect is highly robust: it has been reproduced using a variety of procedures and stimuli, and also seems resistant to practice.

Various factors have been implicated in the Stroop effect: relative discriminability of words and colours (Melara and Mounts 1993) and response modality (McClain 1983), to name but two. However, the two most influential theoretical explanations are the speed of processing and the automaticity hypotheses. Speed of processing models (e.g. Morton and Chambers 1973) assume that words are read faster than colours can be named: when information from each dimension conflicts, the word response, arriving first at the output stage, interferes with the colour response, causing the delay in naming colours. The automaticity hypothesis is based on a distinction between automatic and controlled processes. It proposes that reading words is a strongly automatic process which is involuntary and makes no attentional demands, whereas naming colours is a relatively controlled process, subject to conscious intent and requiring attention. Again, when word and colour responses are different, the more automatic process of word reading interferes with and delays colour naming. It is suggested that word reading is more automatic because we have much more experience at it, an explanation which resembles that put forward by Stroop himself.

Both the speed of processing and the automaticity accounts assign a crucial role to competition between conflicting responses: according to Posner and Snyder (1975, cited in MacLeod 1991), 'the usual Stroop effect arises because of response competition between vocal responses to the printed word and the ink colour'. This response conflict hypothesis also assumes that attention plays no part, with all potential responses being processed.

However, more recent research has tended to contradict this theory. Adopting the Gestaltist distinction between objects and their properties, Kahneman and Henik (1981) propose that during an initial stage of object discrimination attention is allocated to a particular object, and that only the properties of the selected object are processed automatically. This idea is supported by their finding that the Stroop effect is reduced when the incongruent word and ink colour are spatially separate, even though both are equally visible. Kahneman and Chajcek (1983) also found the Stroop effect to be weaker when one colour-neutral word and one conflicting colour word were displayed with a colour bar than when only the conflicting colour word was displayed with the colour bar. They term this the 'dilution effect', and propose an 'attention-capture' hypothesis to explain it. According to this, the processing of words is constrained by capacity limits, and so only the word first attended to will be processed. This runs counter to the assumption of the response competition theory that all possible word responses will be automatically processed without attention being involved. A similar experiment conducted by Yee and Hunt (1991) supports the general idea of attention capture, although their re-analysis of data for individual subjects leads them to suggest that attention is captured at a conceptual level rather than at a perceptual level, as proposed by Kahneman and Chajcek.
Join now!


The three studies described above all focused on the effect of colour-neutral words and used non-integrated versions of the Stroop stimulus, which tends to produce less interference. MacLeod and Hodder (1998) examined whether their results could be generalised to a standard integrated Stroop stimulus. They found that presenting two different incongruent colour words did not cause significantly more interference in colour naming than two identical incongruent words, and so reject the response conflict view which predicts that more potential responses would create more competition and hence more interference. Like Kahneman and Henik (1981) and Kahneman and Chajcek (1983), ...

This is a preview of the whole essay