Biomedical subjects

Choongkil Lee

Publications and source records attributed to Choongkil Lee.

4 recordsLinked to original sources

PubMed2005

Changes in visual motion perception before saccadic eye movements.

Execution of a saccadic eye movement influences subsequent motion perception [Park, J., Lee, J., & Lee, C. (2001). Non-veridical visual motion perception immediately after saccades. Vision Research, 41, 3751-3761]. In the current study, we determined the pattern of perceptual changes for visual motion presented before saccades. The accuracy of judging the direction of a moving target was variable depending on the direction of target motion. Based on the pattern of judgment errors, the direction associated with no error, or DNE, could be defined. When a moving target was seen by stationary eyes, the DNE was roughly vertical, and the perceptual judgment for adjacent directions was biased away from the vertical direction. When the same visual motion was seen before horizontal saccades, the DNE shifted in the direction of the impending saccade, and the perceptual judgment of adjacent directions was shifted away from the new DNE, thus, shifting the perceived direction of the vertical in the direction opposite to the saccade. These changes improved the accuracy of direction judgment for visual motion in the visual field ipsiversive to impending saccades. In addition to shift of the DNE, perceptual judgment for oblique directions became near veridical before saccades, which we call the anti-oblique effect. These results suggest that motion perception is dynamically and anisotropically modulated at the time of saccades, and the DNE shift may be a part of processes dynamically reallocating computational resources, improving perceptual performance in advance for sensory events to be acquired by impending saccades.

Adult↗

PubMed2005

Visual motion perception at the time of saccadic eye movements and its relation to spatial mislocalization.

The same retinal image motion can be produced by a variety of combinations of eye and target motion. In natural conditions, extraretinal information disambiguates retinal information for motion perception. By controlling the timing of visual motion with respect to saccades, it was possible to appraise the roles for motion perception of the signal related to saccades occurring in the vicinity of visual motion. When a visual motion was seen before or after a saccade, its perceived direction was biased in the direction opposite to the saccade. The magnitude of the bias depended on the timing of the visual motion with respect to the saccade and the meridian of the visual motion. The bias appears to be independent of the deformation of visual space reported to occur before and after saccades.

Humans↗

PubMed2003

Expansion of visual space after saccadic eye movements.

Human subjects reported the perceived two-dimensional location of a visual target that was briefly presented after a saccade in the absence of visual references. Consistent with previous studies, immediately after horizontal saccades, there was a salient horizontal component in mislocalization in the direction opposite to the saccade. However, the horizontal component in mislocalization was not constant and was larger for targets presented further into the visual field contraversive to the saccade. For the same horizontal saccades, the vertical component in mislocalization was also obvious, and it was larger for targets located further away from the saccade trajectory. The saccadic effects resulted in an overall pattern of mislocalization that could be best described as a two-dimensional expansion of visual space. The point of expansive origin was not associated with the saccade goal, but was shifted from the saccade goal in the direction of the saccade. These results suggest that spatial information processing at the time of saccades reflects topographic interactions between neural activations from saccade execution and the visual target. The configuration of mislocalized positions of single point stimuli along a line was not comparable to the pattern of non-veridical motion perception described by Park, Lee & Lee (2001), indicating that spatial mislocalization and non-veridical motion perception after saccades are independent phenomena.

Adult↗

PubMed2002

Head-free reading of horizontally and vertically arranged texts.

Parameters of eye and head movements and their coordination in reading horizontally and vertically arranged texts were compared. Reading was faster for horizontally arranged than for vertically arranged texts by 24%, primarily due to larger gaze amplitude for horizontal reading, and thus smaller numbers of saccades and fixations. The higher velocity of gaze saccades for given amplitudes in horizontal than vertical reading also contributed to the difference in reading speed. The horizontal bias in reading is at least partly due to the oculomotor system, because the higher velocity for given amplitude of horizontal saccade was also observed in a control experiment devoid of lexical load, in which a sequentially stepping laser target was tracked. The analysis of instantaneous phase of eye and head movements with a new metric derived by the Hilbert transform suggests that eye and head coupling is stronger for vertical than for horizontal direction in both reading and laser-tracking tasks. These results, combined with previous evidence that text familiarity modulates the timing and strength of head movement commands with respect to eye movements (Vis. Res. 39 (1999) 3761), indicate that the coupling strength between eye and head movements is variable depending on the direction of gaze shift and cognitive context.

Adult↗