Moussa Kousa1, Julien Besle1
Department of Psychology, American University of Beirut, Beirut, Lebanon

We evaluated two adaptive methods for fast and reliable measurement of frequency difference limens (DLFs) at multiple base frequencies in naive participants. Our ultimate goal will be to correlate these DLF functions with cortical frequency magnification functions measured in the participants’ primary auditory cortex using fMRI. We first measured DLFs at 8 log-spaced base frequencies [0.2-8 kHz] using the maximum likelihood procedure (MLP; [1]) in 10 participants (2I2AFC task; 5-6 blocks of 30 trials per frequency). The MLP provided unreliable thresholds that varied between consecutive blocks of the same frequency, due to the MLP’s susceptibility to lapses of attention early in a block. Naive participants also found the MLP’s sudden changes in difficulty in the very first trials confusing. We then switched to the Updated Maximum Likelihood procedure (UML; [3]), which has been developed to improve on the MLP’s above weaknesses by simultaneously and adaptively estimating three parameters of the psychometric function (midpoint, slope and lapse rate of attention) and by increasing difficulty more gradually. To verify the validity of the UML thresholds, we compared them to thresholds obtained using the method of constant stimuli (CS) in 14 participants (8S2A task [2]; 8 log-spaced base frequencies between 0.2 and 8 kHz; 2 blocks of 75 trials per frequency per session; session 1: UML, sessions 2&3: UML or CS, counterbalanced across participants). Preliminary results in six participants suggest that the UML and CS procedures yield very similar thresholds, that only 75 trials are necessary to obtain reliable thresholds within a session, but that most participants’ thresholds substantially improved between sessions 1 and 2, suggesting that minimal training remains necessary to obtain accurate thresholds in naive participants