| The ventral visual stream mediates processing of shape, color, and texture information in support of visual object recognition, whereas the dorsal visual stream is responsible for spatial and visuomotor analyses necessary for grasping and manipulating objects. One open question in the literature concerns how, and when, the cognitive system makes use of these different types of information in object-related conceptual decisions.;The three studies that comprise this dissertation used two psychophysical techniques -- continuous flash suppression and backward masking -- to study whether the information that is carried by dorsal stream regions can be used during object-related conceptual decisions. These techniques were used because they differentially activate the visual cortex, providing a way to isolate the processing within the dorsal stream. Furthermore, they induce unconscious processing, reducing neural crosstalk with ventral and prefrontal regions.;Study I demonstrates that dorsal stream information can contribute to our understanding of visually presented (manipulable) objects. Study II shows that this contribution can take place at different levels of processing -- both when participants have to individuate an object, and when they have to place it within a superordinate category. Moreover, the results from this study suggest that this dorsal stream information must be relatively coarse, as it does not carry specific functional information about objects. Finally, Study III shows that oblong-shaped stimuli, when processed by the dorsal stream, and irrespective of its semantic category, affect the categorization of manipulable objects. Object elongation may reduce the ambiguity in grasp preparation and confer a strong and reliable grasp signal that can be of use when categorizing manipulable objects. Futhermore, this study shows that when information about semantic-category is retrieved, it supersedes information about object elongation in assisting conceptual decisions about objects.;Taken together, these studies suggest that our cognitive system will use a variety of means to reach a suitable decision. In some circumstances, information about the visuomotor properties of a manipulable object (e.g., its graspability) can be sufficiently informative to be useful to the task at hand, but in the presence of other more diagnostic information, it may be relegated to a more ancillary role. |
