Cortical auditory evoked potentials (P 1 -N 1 -P 2 complex) have been extensively used to understand sound processing in the human auditory system. These cortical auditory evoked potentials (CAEP: electrical potential recorded from the auditory area of the cortex following presentation of acoustic stimulus) are believed to reflect the neural encoding of sound signal (Hillyard & Picton, 1978; Hillyard & Kutas, 1983), but they do not provide any viable information regarding discrimination of sounds. The CAEPs do not index behavioural discrimination (Martin & Boothroyd, 1999; Whiting et al, 1998), rather they provide an index for encoding of acoustic event by the cortical neurons (Hillyard & Picton, 1978; Picton et al, 2000). CAEPs have been recorded using various stimuli, such as tone bursts (Jordan et al, 2003), clicks (Eggermont et al, 1997), synthetic speech stimuli (Sharma et al, 2002), musical notes (Jones et al, 1998) and natural speech stimuli (Tremblay et al, 2003; Kaukoranta et al, 1987). The N1-P2 complex is seen in the average of wave- forms recorded for simple sound stimuli, such as tone bursts and clicks. However, it has been noticed that for a complex stimulus with acoustic change/s within the ongoing sound stimulus, multiple overlapping N1-P2 complexes were recorded (Naatanen & Picton, 1987; Kaukoranta et al, 1987; Martin & Boothroyd, 1999). These complexes may be recorded due to change/s in the acoustic proper- ties of the stimulus such as intensity and/or frequency (Naatanen & Picton, 1987; Yingling & Nethercut, 1983), or acoustic changes within a complex sound such as speech (Martin & Boothroyd, 1999; Kaukoranta et al, 1987). This multiple overlapping N1-P2 complex, recorded for a change within an ongoing stimulus at the level of auditory cortex has been termed the acoustic change complex (ACC) (Martin & Boothroyd, 1999). Investigations have suggested that ACC may be a potentially useful tool in the assessment of auditory perception capacity. This assumption has been based on the observations of a good agreement between ACC and subjective measures of intensity discrimination (Martin & Boothroyd, 2000). Its good test-retest reliability in adults (Tremblay et al, 2003) and efficacy in individuals with sensorineural hearing loss (Tremblay et al, 2006), as well as in those with cochlear implants (Lendra & Tremblay, 2006) makes it a viable tool for deter- mining neural encoding abilities. ACC has been recorded for an acoustic stimulus which has changes in its acoustic characteristics that occur relatively after a long time from the onset of stimulus. For the purpose of the present study, the change in stimulus characteristics that takes place in an ongoing sig- nal will be called transition. Duration of the stimulus from its onset to the point of transition is called pre-transition duration. Similarly, for a consonant-vowel syllable, the consonant portion will be called pre-transition duration. ACC has been recorded using speech and non-speech stimuli such as consonant-vowel transition (Kaukoranta et al, 1987; Ostroff et al, 1998; Tremblay et al, 2006), periodi- city changes (Martin & Boothroyd, 1999), amplitude and spectral Original Article Effect of pre-transition stimulus duration on acoustic change complex M. K. Ganapathy * , Vijay Kumar Narne * , Mohan Kumar Kalaiah † & P. Manjula * * Department of Audiology, All India Institute of Speech and Hearing, Mysore University, Karnataka, India, and † Department of Audiology and Speech Pathology, Kasturba Medical College, Manipal University, India Abstract Objective: To investigate the effect of pre-transition duration on acoustic change complex (ACC) for speech and tonal stimulus. Design: Cortical potentials were recorded for consonant-vowel syllable and tonal complex stimuli with varying pre-transition durations. Study sample: Ten individuals (three male and seven female) in the age range from 18 to 26 years, with normal hearing sensitivity, participated in the study. Results: The results revealed that a minimum pre-transition duration of 100 ms for tonal stimulus (with spectral change) and 80 ms for consonant-vowel syllable is necessary in order to elicit ACC. The latency of N1 1 and P2 1 , which is the response for change within the ongoing stimulus, increased with increase in pre-transition duration. The amplitude of the evoked responses did not show any significant change. Conclusions: It was found that minimum pre-transition duration required in eliciting ACC for speech and non-speech stimulus is not same. The speech stimulus required lesser duration of pre-transition than non-speech stimulus. Further studies regarding the acoustic aspects of sound on CAEP in isolation are warranted. Key Words: Acoustic change complex (ACC); pre-transition Correspondence: M. K. Ganapathy, Department of Audiology, All India Institute of Speech and Hearing, Mysore, Karnataka, India. E-mail: ganapathy.mk8@gmail.com (Received 6 February 2012; accepted 17 December 2012) ISSN 1499-2027 print/ISSN 1708-8186 online © 2013 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society DOI: 10.3109/14992027.2012.760850 International Journal of Audiology 2013; 52: 350–359