LETTER RECOGNITION REVEALS PATHWAYS OF 2ND-ORDER AND 3RD-ORDER MOTION

How are second-order (texture-defined) and third-order (pattern-tracki ng) motions processed in our brains? As shown here in the context of a n ambiguous motion task involving a nominal second-order stimuli first devised by Werkhoven ct al., [Werkhoven, P., Sperling, G, & Chubb, C, (1993) Vision Res. 33, 463-485.], the observers fell into two distinc t groups based on the direction of perceived motion, The differences w ere interpreted in terms of the algorithms used to extract motion: one group by using a second-order motion process and the other by using a third-order motion process, This was investigated further using a dua l-task paradigm in which the interference between two tasks indicated the nature of processing involved, Observers who used third-order moti on processing experienced interference with letter recognition and a m ore severe interference in dual third-order motion tasks, Observers wh o used second-order motion processing experienced interference with an other second-order motion detection but not with letter recognition, I nsofar as task interference implies the need for attention, the comple x interference effects and the apparently paradoxical interference eff ects of second-order motion perception imply that there are multiple f orms of attention, Whether two tasks interfere depends on whether they require the same form of attention, Insofar as spatio-temporal proces sing is assumed to be carried out in the dorsal stream and pattern rec ognition in the ventral stream, the interference patterns suggest that second-order motion may be computed entirely in the dorsal stream, an d third-order motion may involve two computational processes, one of w hich shares computational resources with the letter recognition task i n the ventral stream.