Pitch and loudness information encoded in auditory imagery as revealed by event-related potentials JIANHUI WU, a ZULIN YU, b XIAOQIN MAI, c JINGHAN WEI, a and YUEJIA LUO d a Institute of Psychology, Chinese Academy of Sciences, Beijing, China b State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China c Center for Human Growth and Development, University of Michigan, Ann Arbor, Michigan d State Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, Beijing, China Abstract Two experiments using the ERP method and a task that involved comparing an imagined-S1 (the first stimulus) with a perceived-S2 (the second stimulus) were conducted to investigate whether imagined auditory representations encode pitch and loudness information. It was found that the amplitude of the imagery-related late positive complex (LPC) decreased with pitch but increased with loudness of the imagined sound, which was consistent with amplitude mod- ulations of the auditory perception-related N1 component, thereby providing the first neural evidence that auditory imagery encodes perceptual attributes of auditory experiences. Descriptors: Auditory imagery, Pitch, Loudness, Event-related potentials, Late positive complex The most influential theory of mental imagery is Kosslyn’s de- pictive (picture-like) representation of imagery processing, em- phasizing the close similarities between imagery and perception (Kosslyn, Thompson, & Ganis, 2006). Neuroimaging and neu- ropsychological data indicate that the modality-specific visual and auditory cortex is involved in visual and auditory imagery, respectively (Aleman, Formisano, Koppenhagen, Hagoort, de Haan, & Kahn, 2005; Kraemer, Macrae, Green, & Kelley, 2005; Slotnick, Thompson, & Kosslyn, 2005; for reviews, see Kosslyn, Ganis, & Thompson, 2001; and Kosslyn & Thompson, 2003). In the visual modality, neuroimaging data further indicate that, during visual imagery, spatial information is mapped in the pri- mary visual cortex (Klein, Dubois, Mangin, Kherif, Flandin, et al., 2004; Kosslyn, Thompson, Kim, & Alpert, 1995), pro- viding strong evidence for the depictive theory. In the auditory modality, behavioral studies also indicate that auditory imagery represents perceptual attributes of sound such as loudness and pitch (Farah & Smith, 1983; Intons-Peterson, 1980; for reviews, see Intons-Peterson, 1992; and Hubbard, 2010). In Intons-Pe- terson’s (1980) study, the time required to mentally adjust the loudness of one imagined sound to that of another imagined sound increased with the distance between the loudness of the imagined sounds, suggesting auditory imagery encodes loudness. Farah and Smith (1983) found that one could detect the target sound at a lower loudness threshold when the pitch of the imag- ined sound is the same as the following target sound, suggesting auditory imagery also encodes pitch. These behavioral results may be confounded by the subject’s knowledge of the task; however, for example, subjects may use their prior knowledge to simulate what would happen in a real-world situation (Pylyshyn, 2002). Evidence from studies of brain activity, which cannot be simulated by a subject’s tacit knowledge, however, is still scarce. The aim of the present study was to provide neural evidence that auditory imagery encodes pitch and loudness information by using the event-related potential (ERP) method. Auditory stim- uli typically elicit an N1 component in the ERP with a peak latency of about 100 ms and a scalp distribution over fronto- central areas. The amplitude of the N1 is related to perception and increases with sound intensity but decreases with sound fre- quency (for a review, see Na¨a¨ta¨nen & Picton, 1987). Previous ERP studies have shown that a late positive complex (LPC) is related to the generation of both visual and auditory imagery (Farah, Peronnet, Weisberg, & Monheit, 1989; Meyer, Elmer, Baumann, & Jancke, 2007; Wu, Mai, Chan, Zheng, & Luo, 2006). In the present study, we investigated whether the ampli- tude modulation of this imagery-related LPC will follow the same pattern as that of the auditory perception-related N1. If imagery is similar to perception, as the depictive theory suggests, the amplitude of the imagery-related LPC should also increase with loudness (the subjective dimension of intensity), but de- crease with pitch (the subjective dimension of frequency) of the imagined sound. We developed a paradigm called ‘‘imagined-S1/perceived-S2 comparison’’ (Wu, Mai, Yu, Qin, & Luo, 2010). Before starting the EEG (electroencephalography) recordings, participants learned to associate each of three visual cues with one of three pure tones varying in pitch (Experiment 1) or loudness (Exper- This work was supported by the NSFC (30930031, 30900442), and the Ministry of Education, China (PCSIRT, IRT0710), and the Project for Young Scientists Fund, IP, CAS (O9CX042004), and the GSCAS (2006). We thank Professor Sun Junxian for the use of the sound-level meter and Justin Ryder for his editorial assistance. Address correspondence to: Yue-jia Luo, State Key Laboratory of Cognitive Neuroscience and Learning, Beijing Normal University, 19 Xin Jie Kou Wai Street, Beijing, 100875, China. E-mail: luoyj@bnu. edu.cn Psychophysiology, 48 (2011), 415–419. Wiley Periodicals, Inc. Printed in the USA. Copyright r 2010 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2010.01070.x 415