Numerosity judgments in peripheral vision: limitations of the cortical magnification hypothesis.

We studied visual numerosity judgments for linear dot arrays with regular spacing under central and off-axis observation conditions. Results indicate that an appropriate increase in stimulus size, as determined by the human cortical magnification factor, may compensate for the retinal inhomogeneity of numerosity judgments. Such a compensation, however, is no longer possible if in the numerosity judgments observers are deprived of the cue of overall dot-array length. Thus, there are aspects of the relative insensitivity of peripheral visual function that are not captured by purely geometrical considerations of the retino-cortical projection.