Localizing the cortical region mediating visual awareness of object identity

Abstract

Presentations of pictures that are too brief to be recognized, or even guessed above chance on a forced-choice test, nonetheless can facilitate the recognition of the same pictures many trials later. This subliminal visual priming was compared for images translated 4. 8 degrees either Within or Between quadrants of the visual field. Priming was evident only for images that remained within the same quadrant in priming and test trials. Consequently, subliminal visual priming is likely mediated by cortical areas in which cells have receptive fields large enough to respond to both presentations of a stimulus translated almost 5 degrees, yet where the receptive fields are confined to a single quadrant, namely, the human homologue of macaque V4 or TEO (the posterior part of the inferior temporal cortex). Awareness of object identity might therefore be associated exclusively with activity at or beyond the anterior part of the inferior temporal cortex, namely, area TE.

Figure 1

Images of the first (prime) block were presented in the second block in a position translated by 4.8° from their initial position. Translation placed images either within the same visual quadrant in which they were presented in the first block, or in a different quadrant. (drawn to scale.)

Figure 2

Percent correct naming by 64 subjects. Repeating the same image within the same quadrant improved identification markedly. However, when objects were translated to a different quadrant, naming accuracy was only slightly higher than that for control images in the second block. When we consider only the objects that were not identified correctly in block 1, the identification rates in the second block were 42.5% for the Within Quadrant condition, and 23.2% for the Between Quadrants condition. These results were replicated in a second experiment, with a different group of 48 subjects (Fig. 3). Subliminal visual priming therefore is quadrant-specific.

Figure 3

Percent correct naming by 48 subjects participated in the second 4AFC experiment. After each trial in the first block, a 4AFC test was administrated. For images that could not be named when initially shown, accuracy on the subsequent 4AFC test was 31.6%. Images correctly named were always responded to correctly on the 4AFC test. Again, repeating the same image within the same quadrant improved identification markedly, whereas when objects were translated to a different quadrant naming accuracy was only slightly higher than that for control images in the second block. When we consider only the objects that were not identified correctly in block 1, the identification rates in the second block were 42.4% for the Within Quadrant condition, and 27.5% for the Between Quadrants condition. This replicates the results of experiment 1.