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 o blique orientations was studied in blindfolded sighted adults in an explora tion-reproduction task. The purpose was to determine whether the variations of the memorization conditions between the exploration and reproduction ph ases would influence the global performance and the oblique effect (lower p erformance 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 th e length and the nature of the delay in two tasks in which previous researc h has shown that the availability of gravitational cues affected orientatio n coding. Blindfolded adults were asked to explore haptically a rod with minimal (Exp t 1) or natural (Expt 2) gravitational cues and then to reproduce the orien tation 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 ha ptic interpolated tasks. When the delay was unfilled, whatever its length ( 5 s or 30 s), the performance depended on the conditions of manual explorat ion: the oblique effect was absent when the gravitational cues were minimal (Expt 1) and was present when these cues were natural (Expt 2). By contras t, when the delay was filled with interpolated tasks, the haptic oblique ef fect was present whatever the conditions of manual exploration. Taken toget her, these results showed that memorization conditions played a role in the haptic processing of orientations and in the oblique effect when the gravi tational cues were minimal during manual exploration.