No evidence for dorsal-stream-based priming under continuous flash suppression

Previous studies have proposed that potentially action-relevant visual features of masked images are processed along the dorsal visual pathway, and can thus prime responses to images of man-made manipulable objects (tools). According to the “category priming by elongation” hypothesis, (invisible) stimulus elongation is the basis for how the dorsal stream can affect the categorization of tools. In our study, prime stimuli were rendered invisible using continuous flash suppression (CFS) and anaglyphs for dichoptic stimulation. We found that participants' reaction times were only weakly affected by CF-suppressed prime stimuli. If anything, the RT data were more consistent with response priming based on shape. Moreover, when prime visibility was low, participants were not able to infer the prime's category but its shape. We recommend that future CFS priming studies should use crosstalk-free setups for dichoptic stimulation, and that awareness measures should be tailored to the stimulus feature of interest.