Gender Differences in Auditory Adaptation

The relationship between the physical intensity of a stimulus and the perception of that stimulus has been studied empirically since the 1860s. One example of such an empirically-derived relationship is Stevens’ Power Law of Sensation (ψ = kφ). Stevens’ Law relates the physical intensity (φ) of a stimulus to the perception of that stimulus (ψ). For the modality of audition, for example, loudness (ψ) is a function of the intensity (φ) of the auditory stimulus just as the saltiness of a solution (ψ) is a function of the saline concentration (φ) of that solution. The exponent (n) varies between modalities and is usually determined empirically. In contrast to the empirically derived, individual sensory laws, the entropic theory of perception [1] was developed several decades ago as a conceptual unification of many of the empirical sensory laws; this unification gave a theoretical basis for sensory laws that until that time had only been examined empirically. As with Stevens’ Law, entropy theory generalizes across modalities. It also utilizes many of the variables already familiar to us, (physical intensity, φ, the perceptual variable, ψ, and the exponent, n). Sensory phenomena occur in the time domain and entropy theory also includes time as a variable, allowing for a description of time-sensitive sensory phenomona such as auditory adaptation (the decrease in loudness perception to a sustained auditory stimulus). Many of the empirical sensory laws, including Stevens’ Law, can be derived from entropy theory. Previous studies [2] suggest that gender differences exist in the exponent (n) found in Stevens’ Law governing loudness. Using entropy theory, a gender difference in the loudness exponent, present in Stevens’ Law, allowed us to postulate the existence of gender differences in other sensory phenomena encompassed by entropy theory. We developed the following hypothesis: the amount of loudness adaptation measured in female and male listeners over the same time course will differ when pure tones of constant intensity and frequency are administered. Extensive studies of both physiological and psychophysical differences in the female and male human auditory system have been reported [3], e.g. females exhibit greater amplitude and shorter latency in Wave V of the auditory brain-stem response and males experience greater permanent, noise-induced hearing loss. Since there have been no known reports of gender differences in auditory adaptation, an experimental protocol was developed to test this hypothesis. One method of measuring the magnitude of adaptation is to apply a constant-intensity tone to the adapting ear, while retaining in silence the contralateral control ear; this method is termed simultaneous dichotic loudness balance (SDLB) (e.g. [4, 5]). At intervals after the start of the steady tone, the participant is required to adjust the intensity of the tone in the control ear until its loudness matches the loudness in the adapting ear. Adaptation is measured as the intensity difference, in decibels, at the control ear when the tone is initially presented to the adapting ear and at a later time point, t, for t equal to 1, 2, . , 6 min. Preliminary test results suggest that gender differences exist in the rate and extent of auditory adaptation. This adaptation process can be hazardous since decreases in loudness perception allow prolonged exposure to potentially harmful sounds; this prolonged exposure has been identified as a common cause of hearing loss [6].