Abstract
Purpose. Object- and space-based visual processing involves two dynamically interactive systems. Both object- and space-based system activation results from complex interactions of top-down and bottom-up inputs The present study explores the interaction of these systems as processing shifts from one stimulus to another in a bottom-up driven manner dependent on the spatial frequency (SF) of the stimuli.
Methods. Participants responded to the onset of a single SF and to the onset of the second of two SFs presented in succession in separate blocks of trials. Stimuli were Gabor patches of 0.5, 1.0, 4.0, and 12.0 cpd always presented at fixation. In the single-patch condition, one of the four SFs was randomly presented each trial. In the two-patch condition, one of the SFs appeared briefly (either 200 or 500 ms) followed by a target SF. The SF of the first and second patches was always different. All possible combinations of first patch SF and duration and second patch SF were randomly presented. Single-patch RTs were used as a baseline and subtracted from the RTs in the two-patch conditions. These difference scores allowed us to examine the influence preceding SFs had on the response to the target SFs.
Results. Analyses of the differences scores for each target SF were conducted as a function of the first patch SF. The patterns of differences scores as a function of first patch SF were significantly different for 1.0, 4.0, and 12.0 cpd targets but not for the 0.5 cpd target. The results cannot be based on SF discriminability and indicate differences in the SF tuning of the object- and space-based systems.
Conclusions. Object- and space-based visual processing systems may be activated differently depending on the spatial frequency content of stimuli. These differences may allow us to examine the interaction of these systems as processing shifts from one stimulus to another in a bottom-up driven fashion.