Regarding baseballs, the problem is that the fovea can focus on only a very small area only about 2 degrees of the visual field (or an area smaller than your thumbnail held at arm's length)—so as a pitched ball moves closer it can easily slip into your peripheral vision as it becomes larger.
Humphrey static perimetry revealed a severe decrease in sensitivity within the central 30 degrees of the visual field in both eyes (Fig. 1A).
These 'small target motion detectors' (STMDs) were found to be exquisitely selective for small targets subtending no more than a few degrees of the visual field, equivalent to just one or two 'pixels' of the compound eye.
Importantly, however, the type and extent (in degrees) of the visual perturbations were the same for both imaging modalities.
Targets were in one of the 19 areas within the central 30 degrees of the visual field.
The centering fixation stimuli were composed of brightly-colored moving abstract figures and subtended 5 degrees of the visual angle.
In addition, 56 static points (14 per quadrant) were assessed within the central 30 degrees of the visual field using the I4e target.
Static perimetry, which is employed in modern standard automated perimetry (SAP) devices, uses light targets of varied luminance at preset locations typically within the central 30 degrees of the visual field (VF) [ 2].
The magnitude of the crowding phenomenon or contour interaction in foveal vision (comprising only two degrees of the visual field) can be quantified in two aspects: 1) the maximum distance over which interaction occurs (extent) and 2) the amount of loss in acuity (magnitude) [ 2].
Weisman (1981) argues that the environment legibility depends on several key features such as the differentiation between different areas, the degree of visual access, the complexity of spatial layout and the signals.
