Academic journal article Attention, Perception and Psychophysics

The Auditory Redundant Signals Effect: An Influence of Number of Stimuli or Number of Percepts?

Academic journal article Attention, Perception and Psychophysics

The Auditory Redundant Signals Effect: An Influence of Number of Stimuli or Number of Percepts?

Article excerpt

In two experiments, we examined simple reaction times (RTs) for detection of the onsets and offsets of auditory stimuli. Both experiments assessed the redundant signals effect (RSE), which is traditionally defined as the reduction in RT associated with the presentation of two redundant stimuli, rather than a single stimulus. In Experiment 1, with two identical tones presented via headphones to the left ear, right ear, or both, no RSE was found in responding to tone onsets, but a large RSE was found in responding to their offsets. In Experiment 2, with a pure tone and white noise as the two stimulus alternatives, RSEs were found for responding to both onsets and offsets. The results support the notion that the occurrence of an RSE depends on the number of percepts, rather than the number of stimuli, and on the requirement to respond to stimulus onsets versus offsets. The parallel grains model (Miller & Ulrich, 2003) provides one possible account of this pattern of results.

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When participants are asked to respond as quickly as possible to the onset of any stimulus in a simple reaction time (RT) task, RT usually decreases with an increasing number of stimuli (e.g., Hershenson, 1962). This gain in RT with redundant stimuli has been termed the redundant signals effect (RSE) and has been observed with redundant stimuli within the visual (e.g., Corballis, 2002; Fischer & Miller, 2008; Miller, 1982; Mordkoff & Yantis, 1991, 1993; Schwarz, 1994) and the auditory (Schröter, Ulrich, & Miller, 2007) modalities, with redundant bimodal stimuli such as a tone and a light (e.g., Diederich & Colonius, 1987; Giray & Ulrich, 1993) or a light and an electrical pulse (e.g., Forster, Cavina-Pratesi, Aglioti, & Berlucchi, 2002; Gondan, Lange, Rösler, & Röder, 2004), and with redundant trimodal stimuli such as a tone, a light, and a tactile vibration stimulus (Diederich & Colonius, 2004).

Raab (1962) explained this effect in terms of statistical facilitation. According to his race model, each stimulus is processed separately. In trials with redundant stimuli, the stimuli are processed in parallel, and a response is triggered as soon as the first stimulus is detected. Therefore, the RT is determined by the latency of a single detection process in trials with one stimulus, whereas it is determined by the winner of the parallel ongoing detection processes in trials with redundant stimuli. Since the average time of the winner in a race is usually shorter than the average detection time of each single process, this race model predicts an RT advantage for trials with redundant stimuli, as compared with trials with only one stimulus.

Subsequent research provided strong evidence for the notion that the RSE is often too large to be explained by mere statistical facilitation. Therefore, it has been suggested that the activations emerging from the redundant stimuli are somehow combined and that this combined activation triggers the response (Miller, 1982). Several quantitative models have been developed to describe this combination of information and the facilitation in RT that results from such coactivation processes (e.g., Colonius & Arndt, 2001; Colonius & Diederich, 2004; Miller & Ulrich, 2003; Schwarz, 1989, 1994; Townsend & Nozawa, 1997).

Interestingly, there is evidence that the occurrence of an RSE does not depend on the number of physical stimuli and, thus, on the number of activated receptors but, rather, on the number of percepts associated with those stimuli. In a series of simple RT experiments by Schröter et al. (2007), participants were asked to respond to the onsets of auditory stimuli that were presented via headphones to the left ear, the right ear, or both ears. In one experiment, pure tones of identical frequencies were presented to the two ears (i.e., diotic presentation). Previous research has shown that two simultaneously presented identical auditory stimuli, each delivered to one ear via headphones, are not perceived as two separate stimuli but, rather, produce the phenomenal impression of a single auditory percept localized between the two ears (e. …

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