Masayoshi Nagai

The pointedness effect on representational momentum

An observer’s memory for the final position of a moving object is shifted forward in the direction of that object’s motion. It is called representational momentum (RM). This study addressed stimulusspecific effects on RM. In Experiment 1, participants showed larger memory shift for an object moving in its typical direction of motion than when it moved in a nontypical direction of motion. In Experiment 2, participants indicated larger memory shift for a pointed pattern moving in the direction of its point than when it moved in the opposite direction. In Experiment 3, we again examined the influences of knowledge about object’s typical motions and the pointedness of objects, because we did not control the shape (pointedness) of objects in Experiment 1. The results showed that only pointedness affected the magnitude of memory shift and that the effect was smaller than the momentum effect.

Larger forward memory displacement in the direction of gravity

An observers memory for the final position of a moving stimulus is shifted forward in the direction of its motion. Observers in an upright posture typically show a larger forward memory displacement for a physically downward motion than for a physically upward motion of a stimulus (representational gravity; Hubbard & Bharucha, 1988). We examined whether representational gravity occurred along the environmentally vertical axis or the egocentrically vertical axis. In Experiment 1 observers in either upright or prone postures viewed egocentrically upward and downward motions of a stimulus. Egocentrically downward effects were observed only in the upright posture. In Experiment 2 observers in either upright or prone postures viewed approaching and receding motions of a stimulus along the line of sight. Only in the prone posture did the receding motion produce a larger forward memory displacement than the approaching motion. These results indicate that representational gravity depends not on the egocentric axis but on the environmental axis.

Inhibition of target detection in apparent motion trajectory

Letter discrimination performance is degraded when a letter is presented within an apparent motion (AM) trajectory of a spot. This finding suggests that the internal representation of AM stimuli can perceptually interact with other stimuli. In this study, we demonstrated that AM interference could also occur for pattern detection. We found that target (Gabor patch) detection performance was degraded within an AM trajectory. Further, this AM interference weakened when the differences in orientation between the AM stimuli and target became greater. We also revealed that AM interference occurred for the target with spatiotemporally intermediate orientations of the inducers that changed their orientation during AM. In contrast, the differences in phase among the stimuli did not affect the occurrence of AM interference. These findings suggest that AM stimuli and their internal representations affect lower visual processes involved in detecting a pattern in the AM trajectory and that the internal object representation of an AM stimulus selectively reflects and maintains the stimulus attribute.

Comparing face processing strategies between typically-developed observers and observers with autism using sub-sampled-pixels presentation in response classification technique.

In the present study we modified the standard classification image method by subsampling visual stimuli to provide us with a technique capable of examining an individuals face-processing strategy in detail with fewer trials. Experiment 1 confirmed that one testing session (1450 trials) was sufficient to produce classification images that were qualitatively similar to those obtained previously with 10,000 trials (Sekuler et al., 2004). Experiment 2 used this method to compare classification images obtained from observers with autism spectrum disorders (ASD) and typically-developing (TD) observers. As was found in Experiment 1, classification images obtained from TD observers suggested that they all discriminated faces based on information conveyed by pixels in the eyes/brow region. In contrast, classification images obtained from ASD observers suggested that they used different perceptual strategies: three out of five ASD observers used a typical strategy of making use of information in the eye/brow region, but two used an atypical strategy that relied on information in the forehead region. The advantage of using the response classification technique is that there is no restriction to specific theoretical perspectives or a priori hypotheses, which enabled us to see unexpected strategies, like ASDs forehead strategy, and thus showed this technique is particularly useful in the examination of special populations.

Exploration of vertical bias in perceptual completion of illusory contours: Threshold measures and response classification

We investigated whether the perceptual completion of illusory contours exhibits a vertical bias (J. Pillow & N. Rubin, 2002). Experiments 1-3 measured completion with Pillow and Rubins shape discrimination procedure, while including novel control conditions to determine if the results were related to perceptual completion per se. These experiments found no evidence for perceptual completion with stimuli used by Pillow and Rubin but did find completion with smaller stimuli that had larger support ratios. However, even when perceptual completion occurred, there was no evidence for a vertical bias in perceptual completion. Experiments 4-5 used the response classification method (B. L. Beard & A. Ahumada, 1998) to determine which local areas were related to illusory contour discrimination in central and peripheral vision. For central stimuli, there was a slight bias favoring completion of vertical contours, although the extent of the bias varied across participants. There was no vertical bias for peripheral stimuli. Overall, although subject to several important caveats, the results obtained with classification images (but not threshold measures) were consistent with the Pillow and Rubins idea that perceptual completion is more difficult when it requires integrating visual features that are on different sides of the vertical meridian.

Illusory motion and representational momentum

When a moving target vanishes abruptly, participants judge its final position as being ahead of its actual final position, in the direction of motion (resentational momentum Freyd & Finke, 1984). In the present study, we presented illusory motion and examined whether or not forward displacement was affected by the perceived direction and speed of the target. Experiments 1A and 1B showed that an illusory direction of movement of a target was perceived, and Experiment 2 showed that an illusory speed of a moving target was observed. However, neither the direction nor the magnitude of forward displacement was affected by these illusions. Therefore, it was suggested that the mechanism underlying forward displacement (or some extrapolation processing) uses different motion signals than does the perceptual mechanism.

Saccadic Compression of Rectangle and Kanizsa Figures: Now You See It, Now You Don't

Background Observers misperceive the location of points within a scene as compressed towards the goal of a saccade. However, recent studies suggest that saccadic compression does not occur for discrete elements such as dots when they are perceived as unified objects like a rectangle. Methodology/Principal Findings We investigated the magnitude of horizontal vs. vertical compression for Kanizsa figure (a collection of discrete elements unified into single perceptual objects by illusory contours) and control rectangle figures. Participants were presented with Kanizsa and control figures and had to decide whether the horizontal or vertical length of stimulus was longer using the two-alternative force choice method. Our findings show that large but not small Kanizsa figures are perceived as compressed, that such compression is large in the horizontal dimension and small or nil in the vertical dimension. In contrast to recent findings, we found no saccadic compression for control rectangles. Conclusions Our data suggest that compression of Kanizsa figure has been overestimated in previous research due to methodological artifacts, and highlight the importance of studying perceptual phenomena by multiple methods.

LAMBDA RESPONSE BY ORIENTATION OF STRIPED PATTERNS

A lambda response is an averaged occipital EEG potential associated with the offsets of saccadic eye movements. In the present experiment, two participants were asked to make horizontal saccades across horizontal or vertical white-black stripes. Analysis of orientations of striped patterns showed horizontal saccades across vertical stripes produced larger amplitudes of the lambda response than did horizontal saccades across horizontal stripes. Therefore, when the lambda response is used as the index of mental workload, it is necessary to take notice of the orientation of stimulus pattern.

Sound can enhance the suppression of visual target detection in apparent motion trajectory

Detection performance is impaired for a visual target presented in an apparent motion (AM) trajectory, and this AM interference weakens when orientation information is inconsistent between the target and AM stimuli. These indicate that the target is perceptually suppressed by internal object representations of AM stimuli established along the AM trajectory. Here, we showed that transient sounds presented together with AM stimuli could enhance the magnitude of AM interference. Furthermore, this auditory effect attenuated when frequencies of the sounds were inconsistent during AM. We also confirmed that the sounds wholly elevated the magnitude of AM interference irrespective of the inconsistency in orientation information between the target and AM stimuli when the saliency of the sounds was maintained. These results suggest that sounds can contribute to the robust establishment and spatiotemporal maintenance of the internal object representation of an AM stimulus.

Space and Time in Perception and Action: Conceptual influence on the flash-lag effect and representational momentum

When judging the position of a moving object, human observers do not perceive and memorize the moving object’s correct position. There are two known phenomena in judged position errors of a moving object, representational momentum (RM) and the flash-lag effect (FLE), both of which we consider here. RM was originally reported by Freyd and Finke (1984). Freyd and colleagues displayed a series of still frames to imply the rotation of a rectangle (e.g., Freyd & Finke 1984, 1985; Freyd & Johnson 1987). Observers saw three views of a rectangle at different rotations about its center, with 250 ms display duration with 250 ms interstimulus interval. The fourth rectangle was presented as a probe 250 ms after the third frame presentation. The rotation of the probe was selected from possible positions symmetrically distributed around the actual third position of rectangle. Observers were asked whether the rectangle in the third frame (the last frame of the motion sequence) was the same orientation as the probe. The results showed that their memory for the third orientation tended to be shifted in the direction of rotation. In other words, the orientation of the probe rectangle had to be rotated slightly further to be judged as being in the same position as the third rectangle. To account for the forward shift of the final position of a stimulus undergoing implied motion, some authors postulate that the dynamics of the representational system follow physical laws, such as momentum (representational momentum; RM Finke & Freyd 1985; Finke et al. 1986; Freyd 1987; Finke & Shyi 1988). RM is a robust effect as observed with smooth object motion and in pointing at the final position of a moving object (e.g., Hubbard & Bharucha 1988). Several variables influence RM (for review, Hubbard 1995b). RM increases with the velocity (e.g., Freyd & Finke 1985; Hubbard & Bharucha 1988; Nagai & Saiki 2005) and acceleration of the moving target (Finke et al. 1986), pointing to the similarity between RM and physical momentum. Hubbard and others demonstrated that RM may reflect physical principles. For example, RM increases downward, in the direction of gravity (Hubbard & Bharucha 1988; 1995a, 1997; Reed & Vinson 1996; Hubbard & Ruppel 1999; Nagai et al. 2002; Vinson & Reed 2002), whereas implied friction between a moving stimulus and an adjoining surface reduces RM (Hubbard 1995a; see also Nagai & Yagi 2001). Moreover, RM is influenced by real-world knowledge of the typical motions of familiar objects (Freyd