INTERNATIONAL CONGRESS ON ACOUSTICS MADRID , 2-7 SEPTEMBER 2007 DIVIDED LISTENING IN AUDITORY

Two experiments examined patterns of performance when listeners were asked to respond to two spoken messages presented simultaneously. In Experiment 1, the level of one message was systematically varied relative to the other. In selective listening trials, listeners reported two keywords from this message. In divided listening trials, listeners were also required to report two keywords from the other message. Responses to the variable-level message were similar in selective and divided listening: there was a monotonic influence of the level of the message, and a beneficial effect of spatial separation of the two sources. Responses to the second message, however, were relatively unaffected by the level or spatial configuration of the sources. In Experiment 2, the two messages were equal-level but were systematically degraded by adding noise. Errors in reporting a particular message were more frequent as the noise level increased, but this increase in errors was more dramatic for the source reported second in divided listening trials. Together, these results support the idea that different strategies underlie the processing of two simultaneous messages. The data are also consistent with the involvement of a volatile sensory trace in divided listening. INTRODUCTION Studies of selective listening to speech show that listeners are generally good at retrieving information from a talker at a location they are attending, but perform poorly when asked to recall messages from unattended locations [1]. However, several studies have indicated that listeners have some capacity to process semantic information from messages outside the immediate focus of attention (see e.g. [2]) and can perform remarkably well at following two separated talkers when they are instructed in advance to do so [3]. Broadbent [4] postulated that auditory immediate memory allows listeners to process simultaneous inputs in a serial fashion. In his model, all incoming sensory information is stored temporarily in a relatively unprocessed state. Selective attention allows an object to be selected and processed further (e.g. identification of semantic content). In the case of simultaneous inputs, it is possible to process one input and then use the sensory trace (if it is still available) to process the other input. He estimated the sensory trace to last for up to a few seconds. If this model of divided listening applies to listeners processing simultaneous messages in an auditory display, there may be differences in how report of the different messages is affected by various parameters of the display. For example, while spatial cues can greatly enhance selective listening to one message in a mixture, it is not clear whether spatial cues also influence the processing of one of the competing messages if it is accessed using immediate memory. In addition, it is not clear how robustly sounds are represented in the sensory trace. It may be that the processing of a message via the sensory trace mode may be more susceptible to the quality of the acoustic input than the processing of a message using selective attention. Here, two separate experiments are summarised that examined divided listening in auditory speech displays. They provide some preliminary data about how the report of two messages is affected by the context of the display. Experiment 1 focused on the effect of spatial separation in a divided listening task, while Experiment 2 examined whether degradations of the acoustic stimuli differentially affect performance for the two messages.