The ability to perceive motion is a really important ability in human being. While it seems to be natural and easy for us to see and predict motion direction, there are reports that some patients could not see movements (Zihl, Von Cramon, & Mai, 1983). Besides, people can also easily perceive motion from stationary stimuli that are presented at different locations sequentially, typically called apparent motion (Green, 1983; Petersik, 1989, see the right figure as an example). I am interested in studying the input and algorithm people used to perceive motion.
There are multiple sources of information in stimuli that could provide motion signal. Some lower-level signals include transient changes of luminance values in the spatial-temporal domain, and some higher-level signals include objects' position change across time (Reichardt, 1961; Van Santen & Sperling, 1984; Adelson & Bergen, 1985; Cavanagh, 1992). In this series of projects, I am specifically interested in when and how different signals are utilized in motion perception, and what the corresponding processing mechanisms are.
I took the advantage of spatial crowding to study this question. When a target object is presented in the peripheral visual field, other surrounding objects will decrease the spatial resolution at the target location. This spatial crowding effect should affect the availability of the higher-level motion signal, while kept the amount of the lower-level motion signal about the same. By comparing people's motion directional judgment accuracy under crowded and uncrowded conditions, we found that crowding would impair motion perception for slow, but not fast motion stimuli. These results suggest that for slow motion, the higher-level motion signal is necessary for a successful direction judgment.
I took the advantage of spatial crowding to study this question. When a target object is presented in the peripheral visual field, other surrounding objects will decrease the spatial resolution at the target location. This spatial crowding effect should affect the availability of the higher-level motion signal, while kept the amount of the lower-level motion signal about the same. By comparing people's motion directional judgment accuracy under crowded and uncrowded conditions, we found that crowding would impair motion perception for slow, but not fast motion stimuli. These results suggest that for slow motion, the higher-level motion signal is necessary for a successful direction judgment.
We also applied spatial crowding to some other types of motion stimuli, e.g. the Ternus Display. The Ternus Display is known to elicit percepts of element motion (one object moving with two stationary middle objects, see what the Jerrys are doing in the upper right figure) or group motion (all three objects moving together, see what the Jerrys are doing in the middle left figure). We found that with the same display setting, spatial crowding would bias participants to report more element motion, while under uncrowded condition group motion was reported predominantly. Therefore, Ternus percepts are the outputs of independent motion systems, differentially reliant upon low-level transients vs. object position representations. |
To better understand human motion perception, I am also testing a patient with bilateral parietal lobe damage. Due to the damage, the patient's object localization ability is impaired, but only in the upper left visual field. Therefore, this patient provides a great opportunity to test the role of the localization system in motion perception, with his upper right visual field as his own control. We are currently testing him with different motion stimuli to systematically study the role of the higher-level localization system in motion perception.
Relevant papers and presentations:
Ma, Z., McCloskey, M., & Flombaum, J. I. (in press). A deficit perceiving slow motion after brain damage and a parallel deficit induced by crowding. Journal of Experimental Psychology: Human Perception and Performance.
Ma, Z., Niño, J., Hock, H., McCloskey, M., & Flombaum, J. I. (2013). A taxonomy of directional motion judgment based on informational content:
Evidence from a deficit following bilateral parietal brain damage. Visual Cognition. doi: 10.1080/13506285.2013.844964
Ma. Z., McCloskey, M., & Flombaum, J. I. (2014). Differentiating between object-dependent and transient-dependent motion percepts through
crowding. VSS Annual Meeting, St. Pete Beach, Florida, USA
Relevant papers and presentations:
Ma, Z., McCloskey, M., & Flombaum, J. I. (in press). A deficit perceiving slow motion after brain damage and a parallel deficit induced by crowding. Journal of Experimental Psychology: Human Perception and Performance.
Ma, Z., Niño, J., Hock, H., McCloskey, M., & Flombaum, J. I. (2013). A taxonomy of directional motion judgment based on informational content:
Evidence from a deficit following bilateral parietal brain damage. Visual Cognition. doi: 10.1080/13506285.2013.844964
Ma. Z., McCloskey, M., & Flombaum, J. I. (2014). Differentiating between object-dependent and transient-dependent motion percepts through
crowding. VSS Annual Meeting, St. Pete Beach, Florida, USA