Figure 1.

Hybrid images composed of two components were produced using techniques summarized in Figs. 2A and 3A. Regardless of hybrid type, the contrast of each of the two components could be varied over time, with the temporal pattern of contrast modulations being either identical for the two components (synchronized) or uncorrelated for the two (unsynchronized). For each stimulus presentation, seven different contrast values were presented in immediate succession (no blank interval), with each successive contrast value selected at random without replacement. These contrast modulations were always centered about a value of 0.3 rms, the step-size between contrast values was constant in log units and the contrast range (maximum–minimum contrast values in the temporal sequence) was varied to manipulate the discriminability of synchronized from unsynchronized presentations. Discrimination was progressively more difficult at smaller contrast ranges. Different rates of contrast modulation could be achieved by manipulating the frame duration (where frame refers to presentation of a given contrast level).