How visual experience and task context modulate the use of internal and external spatial coordinate for perception and action.

Recent studies proposed that the use of internal and external coordinate systems for perception and action may be more flexible in congenitally blind when compared to sighted individuals. To investigate this hypothesis further, we asked congenitally blind and sighted people to perform, with the hands uncrossed and crossed over the body midline, a tactile temporal order judgment and an auditory Simon task. Crucially, both tasks were carried out under task instructions either favoring the use of an internal (left vs. right hand) or an external (left vs. right hemispace) frame of reference. In the internal condition of the temporal order judgment task, our results replicated previous findings (Röder, Rösler, & Spence, 2004) showing that hand crossing only impaired sighted participants' performance, suggesting that blind people did not activate by default a (conflicting) external frame of reference. However, under external instructions, a decrease of performance was observed in both groups, suggesting that even blind people activated an external coordinate system in this condition. In the Simon task, and in contrast with a previous study (Röder, Kusmierek, Spence, & Schicke, 2007), both groups responded more efficiently when the sound was presented from the same side of the response ("Simon effect") independently of the hands position. This was true under the internal and external conditions, therefore suggesting that blind and sighted by default activated an external coordinate system in this task. Together, these data demonstrated that both sighted and blind individuals were able to activate internal and external information for perception and action