| The mental processes through which we perceive the world have different speeds, which can limit our ability to perceive fast-changing properties of the world as well as our reaction time. Most aspects of visual perception that have been investigated only reflect properties of the world that vary slower than 10 cycles per second (Hz). For example, one cannot determine whether two dots are always the same color or always different colors if they flicker between two colors faster than 10 Hz (100 msec per cycle). This and other results suggests a general slowness for percepts mediated by attention or central processing. However, a few percepts reflect information at temporal frequencies over 30 Hz: percepts of motion direction, flicker, stereodepth, and edges defined by luminance differences. In the present work, we investigated the temporal resolution of the perception of temporal order and simultaneity. When a four-letter sequence was rapidly presented in a single location repeatedly, 75% order thresholds were slower than 190 msec/letter (<3 Hz). In our investigations of simultaneity, in one spatially superposed condition, a leftward-tilted red patch alternated with a rightward-tilted green patch. Observers discriminated between this and a display in which the simultaneous features, or feature pairing, was reversed: a leftward-tilted green patch alternated with a rightward-tilted red patch. 75% thresholds were nearly 20 Hz for this color-orientation pairing, and faster than 30 Hz for brightness-orientation pairings. However, when the features were spatially separated, thresholds fell to less than 3 Hz. Hence, in the absence of other cues, perception of temporal order and simultaneity is limited to slow rates, except when judgments of simultaneity concern spatially superposed features. It seems that specialized perceptual processes provide high temporal resolution access to spatially superposed feature pairings. Moreover, the high temporal resolution suggests that judgments of these pairings are not temporally limited by a binding problem. In contrast, the low temporal resolution of the separated-features simultaneity judgments and the judgments of temporal order suggests that they are limited by central and attentional processing. |
