Binding features of a continuously changing visual stimulus

Consider a disc that changes its color continuously from red to green over time. At the moment when the chromaticity of the continuously changing disc has the appearance of yellow, a second disc of the same chromaticity is presented nearby as a brief pulse. Even though both discs are presented at the same time at the identical chromaticity, the color of the continuously changing disc is perceived to be ahead on the color continuum compared to the pulsed disc (Sheth et al., 2000). Similar results are observed for other features. However, the magnitude of this perceptual shift is different for different features. Here, temporal feature binding of a stimulus with two continuously-changing features was investigated.;Experiment 1 examined how the perceptual-shift times of different features that are part of the same object change during temporal feature binding. The results show that when observers matched both color and orientation simultaneously, the perceptual-shift time for color was significantly longer than for orientation. This result implies that even though two features were part of the same object, they preserved their own perceptual-shift times. Thus, observers perceived the continuously-changing stimulus to have a combination of orientation and color that was never actually presented to the eye.;Experiment 2 examined whether the results of Experiment 1 could be explained by a failure to recognize the two continuously-changing features as being part of the same object. Also, it tested whether color and orientation are more readily bound when orientation is defined by the object's contour rather than a pattern such as gratings. The results were similar to those in Experiment 1. Thus, regardless of whether orientation was defined by gratings or by the object's contour, the perceptual-shift time for color was significantly longer than for orientation.;Experiment 3 examined how transients (caused by either an abrupt onset and offset of a stimulus or by luminance contrast) influence perceptual-shift times during temporal feature binding. The results show significant differences in the magnitude of perceptual-shift times for color and orientation even when temporal transients are eliminated by using a steady stimulus rather than a pulse. Similar results hold when spatial luminance transients were eliminated by using an equiluminant stimulus.;Experiment 4 examined how the rate of change in feature space influenced the perceptual shift times during temporal feature binding. The perceptual shifts in both color and orientation increased with a faster rate of feature change. This result shows that the rate of change in feature space, not physical space, can alter the magnitude of the perceptual-shift time.;Experiment 5 examined whether the particular range of colors used in the experiments influenced perceptual shift times during temporal feature binding. The perceptual-shift times did not depend significantly on the perceived color range.;Experiment 6 tested two hypotheses: extrapolation and postdiction. In the experiments the continuously-changing stimulus varied either only before or only after the presentation of the pulsed stimulus. Perceptual shifts in color were observed with changes either before or after the pulse presentation, while orientation showed perceptual shifts only with changes after the pulse presentation. This suggests that the duration and onset time of a temporal integration window are different for color and orientation.;In sum, the results from the current studies show that features with different perceptual-shift times preserve these different shift times even when the features are part of the same object. This is true regardless of whether the continuously-changing stimulus is compared to a pulsed stimulus or to a steady stimulus. The duration of a temporal integration window, and the time point at which it is initiated, may not be same for different features. Thus, features of the same object are not processed conjointly, resulting in percepts with a combination of perceived features never presented together to the eye.