KE was a 58 year-old factory worker with a high school education who noted an inability to “see” and difficulty in performing routine tasks after suffering a hemorrhagic infarction of the right posterior parietal cortex. KE had suffered an infarction of the left hemisphere causing minor language problems and clumsiness of the right hand three years prior to the investigations reported here. MRI at the time of the testing reported here (see Figures 1 and 2) revealed small areas of infarction involving the left middle temporal gyrus, the left middle frontal gyrus and a larger left posterior parietal infarction; additionally, residual effects of a right parietal hemorrhage were also noted. Increased signal in the subcortical white matter of both hemispheres was also noted on T-2 weighted images.

KE was a 58 year-old factory worker with a high school education who noted an inability to “see” and difficulty in performing routine tasks after suffering a hemorrhagic infarction of the right posterior parietal cortex. KE had suffered an infarction of the left hemisphere causing minor language problems and clumsiness of the right hand three years prior to the investigations reported here. MRI at the time of the testing reported here (see Figures 1 and 2) revealed small areas of infarction involving the left middle temporal gyrus, the left middle frontal gyrus and a larger left posterior parietal infarction; additionally, residual effects of a right parietal hemorrhage were also noted. Increased signal in the subcortical white matter of both hemispheres was also noted on T-2 weighted images.

This experiment was modeled on a task reported by Kanwisher, Yin and Wojciulik (Experiment 7, 1999). KE was asked to name two line drawings presented on cards. Stimuli were generated using twenty basic-level objects (e.g., belt). For each object, two different line drawings were selected from the corpus of Snodgrass and Vanderwart (1980) or were generated by the experimenters. There were 20 stimuli in each of the four categories for a total of 80 trials. There were four different types of trials generated by crossing the variables of object identity and visual similarity. In the “Same/High Similarity” (Figure 3a) stimuli included two identical line drawings; in the “Same/Low Similarity” condition stimuli included two visually dissimilar exemplars of the same object (Figure 3b). In the “Different/High Similarity” condition two visually similar but different objects were presented (Figure 3c). Finally, in the “Different/Low Similarity” condition two visually dissimilar different objects were presented (Figure 3d). An example of these stimuli is shown in Figure 3. In this stimulus set, open and closed umbrellas (Figure 3b) were rated by eight normal controls to be significantly less visually similar than the closed umbrella and the carrot (Figure 3c). The mean visual similarity ratings for the 20 visually dissimilar same pairs of objects was significantly lower than the mean ratings for the 20 visually similar but different pairs of objects (p<.01).