Mechanoreceptive submodality channel interactions: psychophysical observations on differential activation of flutter and vibration.

Psychophysical studies on masking of sensations induced by sinusoidal mechanical stimuli were conducted in human subjects to characterize the interactions within and between the submodalities of flutter and vibration. Using a conditioning-test stimulus paradigm, we found that the threshold of a test stimulus was elevated (masking) when the test stimulus was paired with a twice-threshold conditioning stimulus that activated the same submodality. Detection theory analysis further indicated that the observed elevation in threshold resulted in part from a change in stimulus detectability (i.e.d'). In contrast, when the test stimulus and the twice-threshold conditioning stimulus activated different submodalities, no elevation in test stimulus threshold (no masking) was observed. Thus, for stimuli that activate either flutter or vibration, masking (and the inhibitory operations by which it is presumably mediated) is restricted to a given submodality and not distributed across submodalities. This finding suggests that these submodality channels function independently.