Frequency discrimination for pure-tone and modulated stimuli: an evaluation of automatic and computerized test versions.

Abstract

Monaural differential frequency discrimination (delta f/f) was investigated in the 32 ears of 16 normal-hearing young adults, using an automated test of pitch-memory (the AFTD of Grisanti, Boll. Ital. Audiol. Foniatr., 1978, 1, 166-169) wherein S, in analogy with Bekesy audiometry, continuously adjusts the frequency of alternating pure-tone bursts between discriminable-nondiscriminable, and using a computer-driven test of discrimination of frequency modulation (the CTFD of Biondi, E. et al, Comm. LXV Congr. Soc. Ital. ORL Modena, 1978), wherein S presses a button, within a criterion time window, to a brief episode of frequency modulation in a pure tone. F was either 0.5, 1, or 2 kc/s at 40 db HL. An estimate of delta f/f for every test by the CTFD was printed out by the apparatus, while 4 indices of delta f/f by the ATFD were abstracted by hand from various features of the Bekesy-type tracings. Estimates of delta f/f by the CTFD were close to those of the classic study of Shower and Biddulph, but those by the ATFD were rather larger than reported in previous studies of pitch-memory. Student "t" tests revealed that only 5 of 24 comparisons between tests (4 ATFD variables vs 1 CTFD estimate X 2 ears X 3 frequencies) reached the 95% confidence level, while Pearson r's also showed little evidence of significant relationships between the two tests. While the CTFD yields a more precise delta f/f and has other virtues as a research tool, it demands 40-200 min to explore a listener's discriminability in both ears at 5 frequencies. Thus, although the ATFD yields less precise data, and has inherent within it the possibility of the intrusion of undesired psychological factors, it is to be preferred for clinical use since it demands only 15 min of experimental time.