Representation of Visual Location & Orientation

AH: Developmental Deficit in Location and Orientation Perception

AH, a university student with no history of neurological disorders, is profoundly but selectively impaired in perceiving the location and orientation of visual stimuli.  Her errors are highly systematic, involving left-right and up-down reflections (e.g., reaching far to her right for an object far to her left). AH’s performance has implications for hypotheses concerning the organization of the visual system, and suggests novel conclusions about visual location and orientation representations. AH’s reading performance is also remarkable:  Her reading of text appears intact to casual inspection, but she is severely impaired in reading isolated words and sequences of unrelated words.  Results from several experiments indicate that her reading impairments result directly from her visual localization deficit, and that her reasonably intact reading of text reflects skilled on-line compensation for the perceptual deficit. 

McCloskey, M., Rapp, B., Yantis, S., Rubin, G., Bacon, W. F., Dagnelie, G., Gordon, B., Aliminosa, D., Boatman, D. F., Badecker, W., Johnson, D. N., Tusa, R. J., & Palmer, E.  (1995).  A developmental deficit in localizing objects from vision.  Psychological Science, 6, 112-117.

McCloskey, M., & Palmer, E. (1996).  Visual representation of object location: Insights from localization impairments.  Current Directions in Psychological Science, 5, 25-28.

McCloskey, M., & Rapp, B.  (2000).  Attention-referenced visual representations: Evidence from impaired visual localization.  Journal of Experimental Psychology:  Human Perception and Performance, 26, 917-933.

McCloskey, M., & Rapp, B.  (2000).  A visually-based developmental reading deficit.  Journal of Memory and Language, 43, 157-181.

McCloskey, M.  (2004).  Spatial representations and multiple-visual-systems hypotheses:  evidence from a developmental deficit in visual location and orientation processing.  Cortex, 40, 677-694.

BC: Impaired Representation of Orientation

Although perception of orientation has been discussed extensively in the literature, the nature of the underlying mental representations has not been addressed systematically. We investigated orientation perception in BC, a patient with bilateral occipital and parietal cortical damage from a herpes encephalitis infection. Our results show that in addition to general inaccuracy in discriminating and reproducing line orientations, her errors take the form of left-right mirror reflections across a vertical coordinate axis. We propose that at some level(s) of representation line orientations are represented compositionally, such that the direction of a line’s tilt from a vertical reference meridian is coded independently of the magnitude of the tilt. BC’s reflection errors can then be interpreted as resulting from failure to represent the direction of tilt. Reflection errors across a vertical axis were observed both in visual and tactile line orientation tasks, suggesting that the errors arose at a supra-modal level of representation not restricted to vision, or, alternatively, that visual-like representations are being constructed from the tactile input. 

McCloskey, M., Valtonen, J., & Sherman, J.  (2006). Representing orientation: A coordinate-system hypothesis, and evidence from developmental deficits.  Cognitive Neuropsychology, 23, 680-713.

A Coordinate-System Hypothesis of Orientation Representation and Studies of Normal Adults

Stimulus	Orientation Error

We are examining how the orientation of objects is represented in the visual system. Though few studies have been directed towards understanding representations of object orientation, such processes are important for a number of reasons. For example, when a person reaches for an object, he or she must perceive and represent how the object is oriented in order to grasp it appropriately. Also, correctly recognizing certain letters (e.g. b, d) requires accurate processing of orientation. Our research explores a theoretical perspective (McCloskey, Valtonen, and Sherman, 2006) that regards orientation as a relationship between reference frames. The theory makes predictions about the specific types of errors that occur in tasks entailing the perception and memory of object orientation. Emma Gregory has developed several such tasks that allow specific errors to be coded and thus can explain how people represent the orientation of objects. The observed error patterns in experiments with adult participants suggest that parts of representations of orientation can indeed be selectively misrepresented. Moreover, there may be an essential role of object-centered frames of reference in representing orientation, as suggested by orientation errors such as the one shown above, in which the object is reflected across the object's primary axis of elongation.

McCloskey, M., Valtonen, J., & Sherman, J.  (2006). Representing orientation: A coordinate-system hypothesis, and evidence from developmental deficits.  Cognitive Neuropsychology, 23, 680-713.