Both of these auditory evoked potentials responses arise from generators in the thalamo-cortical region of the central auditory system and so you would associate them with objectively assessing thresholds in adults e.g. medico-legal or non-organic hearing loss, or in those with learning difficulties or other challenges that preclude behavioural threshold finding techniques.
Either approach would be perfectly feasible and acceptable. At least two peer-reviewed studies have compared the techniques for time, accuracy and other clinical considerations (Van Maanen and Stappells 2005; Tomlin et al 2006). Although of similar study design, they make opposing recommendations. Van Maanen and Stappells (2005) suggest that 40 Hz ASSR would be the test of choice whereas Tomlin et al (2006) suggest that the N1-P2 response would be the test of choice. Although of similar design, some elements of the study designs may be factors leading to these conclusions. For example, Van Maanen and Stappells provide clear objective “stopping” criteria for the ASSR but not the N1-P2 responses (“by eye”).
What follows is a short list of some of the positive and negative points of the 40 Hz ASSR when set against the N1-P2 response as a way to objectively estimate hearing threshold in adults:
References and caveats
Van Maanen, A and Stappells, DR. (2005) Comparison of multiple auditory steady-state responses (80 versus 40 Hz) and slow cortical potentials for threshold estimation in hearing impaired adults. IJA 44, 613-624.
Tomlin D et al. (2006) A comparison of 40 Hz auditory steady-state response (ASSR) and cortical auditory evoked potential (CAEP) thresholds in awake adult subjects. IJA 45, 580-588.
To learn more about ASSR watch the following webinar
To learn more about the N1-P2 response watch the following webinar