Abstract
We investigated the extent to which motor relevant information is available from images of objects that are suppressed through binocular rivalry. The dorsal object processing stream has been shown to be activated by visible tools, as well as by tools that are suppressed through binocular rivalry (Fang and He, 2005, NN, 10, 1380–1385). Evidence also suggests that visuomotor processes sub-served by the dorsal stream are automatically activated when participants are presented with manipulable objects (e.g., Culham, et al., 2003, EBR, 153(2), 180–189). Motor facilitation has been observed when manipulable objects are presented in such a way that the handles of the objects afford a reaching/grasping action (Tucker and Ellis, 1998, JEP:HPP, 24(3), 830–846) - participants are faster to respond to auditory stimuli with the hand toward which the objects' handles are directed.
In our study, right-handed participants viewed pictures of manipulable objects with their handles directed towards participant's left or right hand. These pictures could either be visible or suppressed. Participants' overt task was to respond, using their left or right hand, to the pitch of an auditory tone presented after the image of the manipulable object was displayed (e.g., low tones/left hand; high tones/right hand). D-prime measures confirmed that participants were unaware of the contents of the suppressed images.
We obtained a motor facilitation effect for both visible and suppressed tools - participants were faster to respond to tones with the hand toward which the handle of the object was oriented. These data suggest that motor relevant information is processed even when it is suppressed. In addition, our effect was present only for right-hand responses. This is in line with recent data that suggests that right-hand, but not left-hand, visually-guided actions are refractory to visual illusions (Gonzalez, Ganel, and Goodale, 2005,VSS Abstracts, 97).
We wish to thank Brandi Newell for her help collecting data. The research reported here was supported by NIH Grant DC04542 to AC. JA was supported by a Fundação Calouste Gulbenkian. BZM was supported by a NSF Graduate Research Fellowship.