The present study examined the efficacy of using audio cues for redundant coding of tactile key clicks simulated with a piezoelectric actuator. The tactile stimuli consisted of six raised cosine pulses at two levels of frequency and three levels of amplitude. An absolute identification experiment was conducted to measure the information transfers associated with the tactile-audio signal set. Results from Condition 1 (C1) provided a baseline measure by employing only the tactile signals. In Conditions 2-4 (C2-C4), supplemental audio signals were used to encode amplitude cues only, frequency cues only, and both amplitude and frequency cues, respectively. The results showed that partial redundant coding of tactile cues with audio signals could increase information transfer, when the cue (amplitude) was not perfectly identifiable with tactile signals alone (C2). When the cue (frequency) was well perceived through tactile signals alone, audio supplemental cues did not improve performance (C3). With redundant coding of both amplitude and frequency cues (C4), audio signals dominated tactile signals. It was also found that increased information transfer was achieved at the cost of increased response time (C2), suggesting increased mental load associated with the processing of multisensory information. Our findings have implications for the design of simulated key-click signals for mobile devices, and the use of multimodal signals for redundant coding of information in general.
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