Mark Chappell - Academia.edu (original) (raw)
Papers by Mark Chappell
The flash-lag effect occurs when an object is flashed adjacent to the path of a smoothly moving o... more The flash-lag effect occurs when an object is flashed adjacent to the path of a smoothly moving object, and abreast of the moving object. The flashed object appears to spatially lag the moving object in the direction of motion. A number of theories of this effect incorporate the ...
We found that for a flash in the middle of the front of a moving visual stimulus the flash-lag il... more We found that for a flash in the middle of the front of a moving visual stimulus the flash-lag illusion was substantially reduced compared with when the flash was displayed in the more usual position to the side of the moving stimulus. Various stimulus arrangements were then used to test for a number of processes which might contribute to this result, and to the flash-lag illusion itself. With two flashes, one at each location, it was determined that the difference in illusions was not due to the relative positions of the two flashes being perceptually distorted by the presence of the moving stimulus. Similarly, temporal order judgements did not reveal a temporal asynchrony between the flashes. Finally, the hypothesis that masking of the 'in-front' flash by the moving object was causing the reduced flash-lag illusion there was tested by similarly masking the lower flash. Again, results did not support this account. Current investigations are pursuing the possibility that inh...
Copyright in individual works within the repository belongs to their authors or publishers. You m... more Copyright in individual works within the repository belongs to their authors or publishers. You may make a print or digital copy of a work for your personal non-commercial use. All other rights are reserved, except for fair dealings or other user rights granted by the ...
Vision Research, 2014
Previous attempts to measure localization bias around a right-angle turn (L-trajectory) have foun... more Previous attempts to measure localization bias around a right-angle turn (L-trajectory) have found either no spatial bias off the trajectory (Whitney, Cavanagh, & Murakami, 2000) or a bias, in different experiments, both 'inside' and 'outside' the trajectory (Nieman, Sheth, & Shimojo, 2010). However, Eagleman and Sejnowski (2007) presented data showing that the perceived location of a brief feature on two moving stimuli could be predicted from the vector sum of their directions after the feature appeared. Such a vector sum with an L-trajectory could predict that the perceived position before the turn should be biased 'sideways' off the trajectory, in the direction of the final motion. With stimuli that particularly facilitated accurate vernier judgments, and measuring bias via the flash-lag illusion, this is indeed what we observed. Our data thus favour Eagleman and Sejnowski's (2007) supposition. Further, the bias occurred before the change in direction, rather than after it, supporting the contention that it is motion after a point being sampled that affects its perception (Bachmann et al., 2003; Eagleman & Sejnowski, 2007; Krekelberg & Lappe, 2000; Nieman, Sheth, & Shimojo, 2010).
Vision Research, 2007
A dual-task paradigm was used to examine the effect of withdrawing attentional and/or cognitive r... more A dual-task paradigm was used to examine the effect of withdrawing attentional and/or cognitive resources from the flash-lag judgment. The flash-lag illusion was larger, and performance in a detection task was generally poorer, under dual-task conditions than in single-task control conditions. These effects were particularly pronounced when decisions in the two tasks were required simultaneously, as compared to when they could be made sequentially. The results suggest that a time-consuming process is involved in the flash-lag decision, of such a nature that prolonging the process increases the magnitude of the illusion.
Perception, 2012
A Vernier-offset illusion induced by rotating lines, introduced by Matin et al (1976 Perception &... more A Vernier-offset illusion induced by rotating lines, introduced by Matin et al (1976 Perception & psychophysics 20 138-142) was re-examined using onset, offset, and reverse trajectories inspired by flash-lag illusion research, with both Vernier and alignment-with-vertical judgments being recorded. The pattern of illusions found was generally in agreement with a differential latency of stimulus ends account described by those authors, although certain variants of modern spatial projection theories, and a differential latency of attribute account, could also accommodate much of the data.
Perception, 2011
A sudden luminance increment on a moving stimulus was perceived significantly along the trajector... more A sudden luminance increment on a moving stimulus was perceived significantly along the trajectory, in the direction of motion, from its displayed position. A nonlinear relationship with stimulus speed, for a Fröhlich-like illusion, but not for the luminance-increment illusion, challenges certain models of spatial mislocalisation and argues for different processes underlying the two illusions.
Journal of Vision, 2010
ABSTRACT No Yes
Journal of Vision, 2010
Determining how the visual system locates moving stimuli continues to be an experimental and theo... more Determining how the visual system locates moving stimuli continues to be an experimental and theoretical challenge. By making a moving visual stimulus equiluminant with its background, and immersing it in luminance noise, the spatial lead it normal enjoys over a flashed stimulus (the flash-lag illusion) was completely eliminated (the illusion was actually reversed for 6 out of 11 participants). As this manipulation is typically used to reduce Magnocellular (M) visual pathway processing, this is strong evidence that processing in this pathway advances the moving stimulus' perceived position. However, when the flashed stimulus was also made equiluminant in luminance noise, the illusion reappeared, indicating that M pathway processing contributed to its perception too. The presence of the illusion when both stimuli were equiluminant in luminance noise indicates that the illusion can be generated in the absence of M cell activation. To explicate the result with moving stimuli, we displayed two adjacent moving stimuli, one luminance-modulated, and the other equiluminant in noise. The latter was perceived to significantly lag the former (an 'M-P-Hess' illusion), and 39% of the difference in flash-lag illusions, with comparable moving stimulus contrasts, could be accounted for by this illusion.
Journal of Vision, 2007
The brightness of a small incremental flash was found to be considerably suppressed in the vicini... more The brightness of a small incremental flash was found to be considerably suppressed in the vicinity of a moving visual stimulus (effect size, d, up to 6) and less so around a stationary stimulus. The pattern of suppression was mapped and extended 3.5 degrees away from a stationary stimulus and 10.5 degrees behind, and ahead of, a moving stimulus. A second experiment found that dark flashes appeared less dark in the presence of an inducing stimulus of either polarity. Combined results suggest that perceived contrast was being suppressed, in all cases by an inducing stimulus of lesser contrast, and in most cases by an inducing stimulus of lesser luminance. These findings were compared with a number of recent models of the perception of the position of moving visual stimuli. These assume that in the wake of such a stimulus, at certain retinal or cortical areas, there is a region of neural inhibition and that, preceding them, there is a (bow-wave-like) region of neural excitation. The current findings confirm the inhibitory, but not the excitatory, assumptions in these theories.
Journal of Vision, 2004
Abstract In Experiment 1 the reversal point of a moving object (12/s) was compared with a station... more Abstract In Experiment 1 the reversal point of a moving object (12/s) was compared with a stationary fixation cross. For five out of six participants the reversing object's trajectory had to extend significantly past the fixation point (0.1) in order for it to appear to reverse on the ...
The flash-lag effect occurs when an object is flashed adjacent to the path of a smoothly moving o... more The flash-lag effect occurs when an object is flashed adjacent to the path of a smoothly moving object, and abreast of the moving object. The flashed object appears to spatially lag the moving object in the direction of motion. A number of theories of this effect incorporate the ...
We found that for a flash in the middle of the front of a moving visual stimulus the flash-lag il... more We found that for a flash in the middle of the front of a moving visual stimulus the flash-lag illusion was substantially reduced compared with when the flash was displayed in the more usual position to the side of the moving stimulus. Various stimulus arrangements were then used to test for a number of processes which might contribute to this result, and to the flash-lag illusion itself. With two flashes, one at each location, it was determined that the difference in illusions was not due to the relative positions of the two flashes being perceptually distorted by the presence of the moving stimulus. Similarly, temporal order judgements did not reveal a temporal asynchrony between the flashes. Finally, the hypothesis that masking of the 'in-front' flash by the moving object was causing the reduced flash-lag illusion there was tested by similarly masking the lower flash. Again, results did not support this account. Current investigations are pursuing the possibility that inh...
Copyright in individual works within the repository belongs to their authors or publishers. You m... more Copyright in individual works within the repository belongs to their authors or publishers. You may make a print or digital copy of a work for your personal non-commercial use. All other rights are reserved, except for fair dealings or other user rights granted by the ...
Vision Research, 2014
Previous attempts to measure localization bias around a right-angle turn (L-trajectory) have foun... more Previous attempts to measure localization bias around a right-angle turn (L-trajectory) have found either no spatial bias off the trajectory (Whitney, Cavanagh, & Murakami, 2000) or a bias, in different experiments, both 'inside' and 'outside' the trajectory (Nieman, Sheth, & Shimojo, 2010). However, Eagleman and Sejnowski (2007) presented data showing that the perceived location of a brief feature on two moving stimuli could be predicted from the vector sum of their directions after the feature appeared. Such a vector sum with an L-trajectory could predict that the perceived position before the turn should be biased 'sideways' off the trajectory, in the direction of the final motion. With stimuli that particularly facilitated accurate vernier judgments, and measuring bias via the flash-lag illusion, this is indeed what we observed. Our data thus favour Eagleman and Sejnowski's (2007) supposition. Further, the bias occurred before the change in direction, rather than after it, supporting the contention that it is motion after a point being sampled that affects its perception (Bachmann et al., 2003; Eagleman & Sejnowski, 2007; Krekelberg & Lappe, 2000; Nieman, Sheth, & Shimojo, 2010).
Vision Research, 2007
A dual-task paradigm was used to examine the effect of withdrawing attentional and/or cognitive r... more A dual-task paradigm was used to examine the effect of withdrawing attentional and/or cognitive resources from the flash-lag judgment. The flash-lag illusion was larger, and performance in a detection task was generally poorer, under dual-task conditions than in single-task control conditions. These effects were particularly pronounced when decisions in the two tasks were required simultaneously, as compared to when they could be made sequentially. The results suggest that a time-consuming process is involved in the flash-lag decision, of such a nature that prolonging the process increases the magnitude of the illusion.
Perception, 2012
A Vernier-offset illusion induced by rotating lines, introduced by Matin et al (1976 Perception &... more A Vernier-offset illusion induced by rotating lines, introduced by Matin et al (1976 Perception & psychophysics 20 138-142) was re-examined using onset, offset, and reverse trajectories inspired by flash-lag illusion research, with both Vernier and alignment-with-vertical judgments being recorded. The pattern of illusions found was generally in agreement with a differential latency of stimulus ends account described by those authors, although certain variants of modern spatial projection theories, and a differential latency of attribute account, could also accommodate much of the data.
Perception, 2011
A sudden luminance increment on a moving stimulus was perceived significantly along the trajector... more A sudden luminance increment on a moving stimulus was perceived significantly along the trajectory, in the direction of motion, from its displayed position. A nonlinear relationship with stimulus speed, for a Fröhlich-like illusion, but not for the luminance-increment illusion, challenges certain models of spatial mislocalisation and argues for different processes underlying the two illusions.
Journal of Vision, 2010
ABSTRACT No Yes
Journal of Vision, 2010
Determining how the visual system locates moving stimuli continues to be an experimental and theo... more Determining how the visual system locates moving stimuli continues to be an experimental and theoretical challenge. By making a moving visual stimulus equiluminant with its background, and immersing it in luminance noise, the spatial lead it normal enjoys over a flashed stimulus (the flash-lag illusion) was completely eliminated (the illusion was actually reversed for 6 out of 11 participants). As this manipulation is typically used to reduce Magnocellular (M) visual pathway processing, this is strong evidence that processing in this pathway advances the moving stimulus' perceived position. However, when the flashed stimulus was also made equiluminant in luminance noise, the illusion reappeared, indicating that M pathway processing contributed to its perception too. The presence of the illusion when both stimuli were equiluminant in luminance noise indicates that the illusion can be generated in the absence of M cell activation. To explicate the result with moving stimuli, we displayed two adjacent moving stimuli, one luminance-modulated, and the other equiluminant in noise. The latter was perceived to significantly lag the former (an 'M-P-Hess' illusion), and 39% of the difference in flash-lag illusions, with comparable moving stimulus contrasts, could be accounted for by this illusion.
Journal of Vision, 2007
The brightness of a small incremental flash was found to be considerably suppressed in the vicini... more The brightness of a small incremental flash was found to be considerably suppressed in the vicinity of a moving visual stimulus (effect size, d, up to 6) and less so around a stationary stimulus. The pattern of suppression was mapped and extended 3.5 degrees away from a stationary stimulus and 10.5 degrees behind, and ahead of, a moving stimulus. A second experiment found that dark flashes appeared less dark in the presence of an inducing stimulus of either polarity. Combined results suggest that perceived contrast was being suppressed, in all cases by an inducing stimulus of lesser contrast, and in most cases by an inducing stimulus of lesser luminance. These findings were compared with a number of recent models of the perception of the position of moving visual stimuli. These assume that in the wake of such a stimulus, at certain retinal or cortical areas, there is a region of neural inhibition and that, preceding them, there is a (bow-wave-like) region of neural excitation. The current findings confirm the inhibitory, but not the excitatory, assumptions in these theories.
Journal of Vision, 2004
Abstract In Experiment 1 the reversal point of a moving object (12/s) was compared with a station... more Abstract In Experiment 1 the reversal point of a moving object (12/s) was compared with a stationary fixation cross. For five out of six participants the reversing object's trajectory had to extend significantly past the fixation point (0.1) in order for it to appear to reverse on the ...