Recognition alters the spatial pattern of FMRI activation in early retinotopic cortex

Abstract

Early retinotopic cortex has traditionally been viewed as containing a veridical representation of the low-level properties of the image, not imbued by high-level interpretation and meaning. Yet several recent results indicate that neural representations in early retinotopic cortex reflect not just the sensory properties of the image, but also the perceived size and brightness of image regions. Here we used functional magnetic resonance imaging pattern analyses to ask whether the representation of an object in early retinotopic cortex changes when the object is recognized compared with when the same stimulus is presented but not recognized. Our data confirmed this hypothesis: the pattern of response in early retinotopic visual cortex to a two-tone "Mooney" image of an object was more similar to the response to the full grayscale photo version of the same image when observers knew what the two-tone image represented than when they did not. Further, in a second experiment, high-level interpretations actually overrode bottom-up stimulus information, such that the pattern of response in early retinotopic cortex to an identified two-tone image was more similar to the response to the photographic version of that stimulus than it was to the response to the identical two-tone image when it was not identified. Our findings are consistent with prior results indicating that perceived size and brightness affect representations in early retinotopic visual cortex and, further, show that even higher-level information--knowledge of object identity--also affects the representation of an object in early retinotopic cortex.

Fig. 1.

Experimental procedure (blocked design). A: during 3 phases of the experiment subjects viewed 1) 2 different 2-tone images that they could not identify (“Mooney1”); 2) the easily identifiable grayscale versions of the same images (“Photo”); 3) the original 2-tone images that could now be easily recognized because of experience with the corresponding photograph (“Mooney2”). B: in experiment 2, 2 images were randomly selected for each subject from the set of 8 images shown here.

Fig. 2.

Regions of interests (ROIs). A: a statistical map for lateral occipital complex (LOC, defined as the region that responded more strongly to images of intact objects than to images of scrambled objects; P < 10⁻⁴) is shown for one representative subject. We selected the 2 regions at the lateral occipital lobe (circled) as LOC. B: inflated cortical surfaces of a brain with dark gray regions representing sulci and light gray regions representing gyri. Foveal confluence (FC) was defined as a small region at the posterior end of the calcarine sulcus (green), functionally constrained to the region (yellow) that responded more strongly to images of intact/scramble objects than to fixation (P < 10⁻²⁵). Another annulus ROI surrounding the FC was also defined (red).

Fig. 3.

Blocked design results. A: the correlation for the 3 comparisons (Mooney1–Photo, Mooney2–Photo, and Mooney2–Mooney1) in LOC. The correlation for Mooney2–Photo is significantly greater than that for Mooney1–Photo (P = 0.010). B: the correlation for the 3 comparisons in the foveal confluence ROI. The correlation for Mooney2–Photo is significantly greater than that for Mooney1–Photo (P = 0.048). Error bars indicate SEs.

Fig. 4.

Event-related results. The correlation for the 3 comparisons (Mooney1–Photo, Mooney2–Photo, and Mooney2–Mooney1) in the foveal confluence ROI. The correlation for Mooney2–Photo is significantly greater than that for Mooney1–Photo (P < 0.001). Error bars indicate SEs.

Fig. 5.

The mean beta weights of the 6 conditions for experiment 1 in (A) LOC and (B) foveal confluence. Error bars indicate SEs.

Fig. 6.

The mean beta weights of the 6 conditions for experiment 2 in the foveal confluence ROI. Error bars indicate SEs.

Fig. 7.

Pattern analysis results in the annulus ROI surrounding the foveal confluence. A: the correlation for the 3 comparisons (Mooney1–Photo, Mooney2–Photo, and Mooney2–Mooney1) in experiment 1. The correlation for Mooney2–Photo is not significantly greater than that for Mooney1–Photo (P = 0.94). B: the correlation for the 3 comparisons in experiment 2. The correlation for Mooney2–Photo is not significantly greater than that for Mooney1–Photo (P = 0.51). Error bars indicate SEs.