| Subjects are better able to identify a spatial, vibrotactile pattern (such as a letter) when it is presented in isolation than when it is presented in the temporal and spatial presence of another pattern, a reduction in performance termed "masking." In general, masking is greatest when the temporal separation between the onset of the pattern to be identified (the target) and the onset of the pattern to be ignored (the masker) is brief, and decreases as the stimulus onset asynchrony (SOA) is increased. Although much is known about the time-course of vibrotactile masking, relatively little is known about the factors underlying masking with vibrotactile stimuli. The results of three experiments suggest that a major factor involved in vibrotactile masking is temporal integration. When two patterns are presented in close temporal and spatial proximity they are integrated, that is, they are combined into a composite. The ability to identify a target pattern is reduced because subjects have difficulty in determining which elements in the composite are contributed by the target, and which elements are contributed by the masker. In addition, the results suggest that the temporally-leading pattern is represented in the composite somewhat less strongly than the temporally-trailing pattern. A model based on the results of these three experiments is proposed, the Integration Model. Two predictions of the model are tested in two additional experiments and receive support (Experiments 4 and 5). One of the implications of the model is that temporal order information at brief SOAs is imperfect. A final experiment, Experiment 6, investigated temporal order effects with sequentially presented vibrotactile patterns. The results showed that at brief SOAs, subjects can correctly recognize the presence of a predetermined target pattern and yet be unable to judge correctly its temporal position. The Integration Model accounts for some additional findings in the literature. These, together with some of the questions and issues raised by the model, are discussed. |
