Academic journal article Perception and Psychophysics

Multisensory Synesthetic Interactions in the Speeded Classification of Visual Size

Academic journal article Perception and Psychophysics

Multisensory Synesthetic Interactions in the Speeded Classification of Visual Size

Article excerpt

In the present study, we attempted to demonstrate a synesthetic relationship between auditory frequency and visual size. In Experiment 1, participants performed a speeded visual size discrimination task in which they had to judge whether a variable-sized disk was bigger or smaller than a standard reference disk. A task-irrelevant sound that was either synesthetically congruent with the relative size of the disk (e.g., a low-frequency sound presented with a bigger disk) or synesthetically incongruent with it (e.g., a low-frequency sound presented with a smaller disk) was sometimes presented together with the variable disk. Reaction times were shorter in the synesthetically congruent condition than in the incongruent condition. Verbal labeling and semantic mediation interpretations of this interaction were explored in Experiment 2, in which high- and low-frequency sounds were presented in separate blocks of trials, and in Experiment 3, in which the tones were replaced by the spoken words "high" and "low." Response priming/bias explanations were ruled out in Experiment 4, in which a synesthetic congruency effect was still reported even when participants made same-versus-different discrimination responses regarding the relative sizes of the two disks. Taken together, these results provide the first empirical demonstration that the relative frequency of an irrelevant sound can influence the speed with which participants judge the size of visual stimuli when the sound varies on a trial-by-trial basis along a synesthetically compatible dimension. The possible cognitive bases for this synesthetic association are also discussed.

The speeded classification paradigm has long been used by psychologists to study a variety of issues in selective attention research (e.g., Garner, 1974; see Marks, 2004, for a recent review). In a typical study, participants have to discriminate one characteristic of a stimulus (e.g., its size) as rapidly as possible while trying to ignore any "irrelevant" characteristics of the stimulus (e.g., its brightness) that may also vary on a trial-by-trial basis (see, e.g., Garner, 1977). Many studies over the last 30 years have shown that a participant's response to the relevant characteristic of a stimulus can be influenced by variations in the irrelevant stimulus dimension, giving rise to what has become known as Garner interference (e.g., Garner, 1974; Pomerantz, Pristach, & Carson, 1989) or congruence effects (e.g., Clark & Brownell, 1975; Patching & Quinlan, 2002).1

These effects have also been demonstrated to occur cross-modally when the relevant and irrelevant stimulus characteristics are presented in different sensory modalities (see, e.g., Bernstein & Edelstein, 1971; Taylor & Campbell, 1976; see Marks, 2004, for a review). For example, Bernstein and Edelstein asked participants to discriminate the side of a display on which a visual stimulus was presented (e.g., left or right) while trying to ignore a simultaneously presented monaural tone. The participants responded more rapidly on trials on which the two stimuli were presented on the same side than on those trials on which they were presented on different sides (but see Spence & McDonald, 2004).

The speeded classification paradigm has also been used across synesthetically defined cross-modal dimensions.2 For instance, Melara and O'Brien (1987) reported a series of experiments in which they explored whether synesthetic correspondences in nonsynesthetic individuals were based on perceptual (rather than allegorical or inferential) interactions. Participants were presented simultaneously with a sequence of visual stimuli whose elevation (e.g., higher vs. lower) varied and a low- or high-frequency tone (174.6 vs. 1046.5 Hz, respectively; see also Pratt, 1930; Stumpf, 1883). Response latencies to classify the elevation of the visual stimuli were longer when the irrelevant tones were synesthetically incongruent with the target (e. …

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