Orienting of attention in humans is believed to occur in two different ways: endogenously (or voluntary) or exogenously (or automatic). In Posner's spatial cueing paradigm, centrally presented predictive symbolic cues decrease the reaction time (RT) to targets when they are indicated correctly in comparison to when they are indicated incorrectly. This RT's difference, called validity effect, appears when the time between the onset of the cue and the onset of the target (stimulus onset asynchrony-SOA) is longer than 100-200 ms. It is suggested that this interval is necessary to orient the attention in a controlled (voluntary) manner. However, recent studies show that validity effect also occurs with shorter SOA (50-100ms). Therefore, it could be hypothesized that the repeated pairing between cue and target (usually 80% of tries) correspond to a form of classical conditioning that contributes to an endogenous validity effect even with SOA around 100 ms, though without voluntary control over this orienting. The aim of the present study is to investigate whether the endogenous orienting of attention involves (1) processes of automatic nature due to repeated pairings between cue and target, and (2) processes of voluntary nature related to an active control of orienting attention. There will be two main groups, divided into four groups, each of them consisting in one group with predictive cue (80/20) and another with non-predictive cue (50/50). Volunteers of the endogenous voluntary orienting of attention group (OEV) will be presented to a temporal signal between the symbolic cue and the target to avoid association between them. After the temporal signal, the volunteer should begin orienting one's attention to the location previously indicated by the cue; at the end of the trial this signal should be reported. The target will be presented with different SOAs after the temporal signal presentation and the volunteer should respond to it by pressing an optic key. Endogenous automatic orienting of attention groups (OEA) will receive the same stimuli. However, for them, the temporal signal will be presented before the symbolic cue. It is expected that OEV-80/20 group show validity effect only with longer SOA (>200 ms), because cue-target pairings were avoided with the insertion of a temporal signal. Also, the OEV-50/50 group is expected to show validity effect with long SOA because the volunteer will orient voluntarily the attention to the location indicated by the cue, thus facilitating the response to targets correctly indicated.
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