3.3.3.f General discussion

The objective of the present study was to find again an attention capture by deviant stimuli, already described by Schröger [1996] in a similar protocol, and to determine whether the concomitant presence of an auditory perception, either endogenous or exogenous, could influence the system underlying automatic deviance detection. The results revealed that a deviant stimulus was able to capture attention whatever the group of participants considered. This suggests the effectiveness and robustness of the preattentive system responsible for attention switching to environmental deviance. Automatic and preattentive selection of information allows us to process some tasks by preventing competition between the relevant information and the irrelevant ones. Selective attention leads to a filtering of sensory inputs to sort out the main information needed to perform accurately the task, and to reject irrelevant information that could disturb the current processing. However, a cognitive function that is parallel to selective attention and that is capable to direct or capture attention toward an unexpected input, without any explicit intention to select this input, is essential for life [Strange et al., 2000]. The auditory system is really specialized for this kind of alerting [Näätänen, 2001].

We had hypothesized that the tinnitus signal could direct and keep attention toward itself. In the present study, only one result might be in favor of this hypothesis. Indeed, unilateral tinnitus participants responded more accurately when the task had to be performed in the tinnitus ear, in comparison with the situation where the task was performed in the non-tinnitus ear. This suggests that the preattentive system responsible for attention switching has difficulty in redirecting attention toward something else than the tinnitus ear. Moreover, this result was not obtained for the tinnitus-simulated participants. We cannot directly compare the populations of participants in our study because of differences in age and auditory status. Nevertheless, taken together, our findings tend to suggest that, first, tinnitus patients present overall cognitive difficulties as revealed by their low reaction times (see “Comparison between groups” section). Some support of a global disturbance of attention processes in tinnitus patients has already been found in a study using a Stroop paradigm [Andersson et al., 2000]. Second, the attentional disturbances induced by tinnitus were not the same as those resulting from the addition of an external noise, even if its physical parameters were specially chosen to make it resemble the tinnitus signal. This is in agreement with the idea that a specific processing is associated with the tinnitus signal, as suggested by several psychological and physiological [Jastreboff, 1990; Moller, 1997; Levine, 1999; Andersson, 2002] models of tinnitus. In cases where tinnitus does not attract attention, or does not affect cognitive processing, it would be expected that habituation takes place, and even that tinnitus no more reaches awareness. Actually, our data tend to show that chronic tinnitus may automatically attract attention. Thus, it seems like, in that case, the attention system is not able to classify the tinnitus signal as an irrelevant information, preventing habituation from taking place. The effect of a larger attention focus in the presence of tinnitus is consistent with previous studies [Jacobson et al., 1995]. However, it seems that the effect observed in the present work is small and that the paradigm used may not be efficient enough to draw out the precise mechanisms responsible for the attractive effect of the tinnitus ear. Some further protocols should be designed to fulfill this goal. This could be a way for a better understanding of the mechanisms underlying habituation to this phantom perception, a step necessary for future therapeutic strategies preventing the persistence of this symptom.

Acknowledgments. We especially thank the subjects who participated in this study. We also thank Tim Greenland for comments on English phrases. This research was supported by funds from the Cognitique ACI from the French Government; project COG 94 entitled “Perturbations du traitement attentionnel et des asymétries centrales dans les acouphènes mal tolérés: exploration et applications thérapeutiques”, financing of 300,000 FF for two years (1999-2000).