ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

3aAO1. Modulation detection interference on presentation of two amplitude-modulated tones.

William F. Dolphin

Dept. of Biomed. Eng., Boston Univ., Boston, MA 02215

Psychophysical studies have shown that the processing of modulation in one frequency channel is interfered with when a similar modulation pattern is present in another frequency channel. To test for physiological correlates to this phenomena a sinusoidally amplitude-modulated (SAM) probe tone was presented in the presence of a simultaneously gated, modulated, or unmodulated interfering tone while recording from the scalp of anesthetized gerbils. Responses were recorded from the scalp, amplified, digitized, and averaged. The amplitude of the response was determined as the magnitude of the Fourier transform measured at the frequency corresponding to the probe f[sub mod] and f[sub c]. Responses in the presence of the interfering tone were compared to responses obtained to the SAM probe tone alone. The shape of the interference pattern was highly dependent on the modulation frequency of the interfering tone. With some modulation frequencies an increase in interference relative to control responses was observed at the probe f[sub mod], while at other modulation frequencies either no interference, or even enhancement of the response was apparent. In contrast, at the probe f[sub c] interference patterns were very similar for all interference tone modulation frequencies.