Role of memorization conditions in the haptic processing of orientations and the 'oblique effect'

The haptic processing of vertical, horizontal, 45 degrees and 135 degrees oblique orientations was studied in blindfolded sighted adults in an exploration-reproduction task. The purpose was to determine whether the variations of the memorization conditions between the exploration and reproduction phases would influence the global performance and the oblique effect (lower performance in oblique orientations than in vertical-horizontal orientations). If orientation coding depended on attentional resources, the increase in memory constraints would affect the haptic processing of orientations and the oblique effect, Memory constraints were therefore varied by changing the length and the nature of the delay in two tasks in which previous research has shown that the availability of gravitational cues affected orientation coding. Blindfolded adults were asked to explore haptically a rod with minimal (Expt 1) or natural (Expt 2) gravitational cues and then to reproduce the orientation of this rod ipsilaterally after one of four memorization conditions: with 5 s or 30 s unfilled delays, and 30 s delays filled with verbal or haptic interpolated tasks. When the delay was unfilled, whatever its length (5 s or 30 s), the performance depended on the conditions of manual exploration: the oblique effect was absent when the gravitational cues were minimal (Expt 1) and was present when these cues were natural (Expt 2). By contrast, when the delay was filled with interpolated tasks, the haptic oblique effect was present whatever the conditions of manual exploration. Taken together, these results showed that memorization conditions played a role in the haptic processing of orientations and in the oblique effect when the gravitational cues were minimal during manual exploration.