Exploring Auditory Category Distinctions in Perception and Imagery

Imagery, the ability to generate perceptual experiences in the absence of external stimuli, is used every day when remembering a past event or imagining a novel situation. While most previous research on imagery has focused on the visual domain, the present study presents an investigation of auditory imagery. The perception of different categories of sound has been shown to evoke different neural responses. Further, the neural processes underlying auditory imagery and perception have been shown to be similar. Therefore, we hypothesized that auditory imagery would rely on similar categorical processing. Participants learned shape-sound associations and were then asked to imagine the matching sound when presented with the associated shape. We chose two example stimuli from two maximally different sound categories — human speech sounds and nonhuman environmental sounds — to investigate our hypothesis. Electroencephalography (EEG) data were recorded while participants listened to and imagined the sounds. The mean voltage in the P2 event-related potential time window (180-280 ms) was significantly larger for perception of the speech sounds than the environmental sounds, and the late positive event-related potential complex (LPC, 350-500 ms) associated with imagery was significantly smaller for imagery of the speech sounds than the environmental sounds. This suggests that, as in perception, the neural processing of imagined sounds is categorical.