Auditory frequency and intensity discrimination in pigmented rats

Auditory function was investigated in seven pigmented hooded rats (strain Long-Evans) with the aid of an operant conditioning procedure. Frequency difference limen was measured at frequencies from 0.5 to 64 kHz at 50 dB sensation level (SL). Weber ratios (frequency difference limen/frequency) in this range varied between 3.7 and 7.3%. The decline in the intensity of the stimulus from 50 to 10 dB SL was accompanied by a slight increase in the frequency difference limen. The frequency difference limen values were similar for frequency shifts upwards or downwards. Intensity discrimination was measured at 50 dB SL at frequencies of 2, 8 and 32 kHz. Intensity difference limen was frequency independent and amounted to 2.9 ± 0.5 dB in conditions of upward intensity shift. The values of intensity difference limen measured in conditions of downward intensity shift were significantly larger and amounted to 6.5 ± 1.6 dB. The characteristics of hearing function found in these experiments correspond with those described by other authors in albino rats and indicate that albinism in the rat has no significant influence on auditory frequency and intensity discrimination.