Saccadic suppression of displacement is strongest in central vision

Perception of target displacement is severely degraded if the displacement occurs during a saccadic eye movement, but the variation of this effect across the visual field is unknown. A small target was displaced from a starting point at the midline, or 10 deg to the right or left, while the eye made a saccade from the 10 deg right position to the 10 deg left position. Saccades were detected and the target displaced on line. Assessed with a signal detection measure, suppression was stronger in central vision than in more peripheral locations for all three subjects. Leftward and rightward displacements yielded equal thresholds. The results complement the findings of others to reveal a picture of perceptual events during saccades, with both deeper saccadic suppression and faster correction of spatial values (the correspondences between retinal position and perceived egocentric direction), favouring more accurate spatial processing in central vision than in the periphery.     

Do diagnostic patterns exist in the sleep behaviors of normal children?

We investigated the factor structure of the Children's Sleep Behavior Scale in an unselected sample of children (N=838), ages 6 to 12.5 years, drawn from an elementary school population. Although no factor emerged that corresponded exactly to the parasomnias, as described by the Association of Sleep Disorders Centers (1979), all of the variables that loaded on Factor 1 were behaviors characteristic of the parasomnias, with the exception of recalled nightmares. Variables that were expected to load on this factor, but did not, were sleeptalking, teeth grinding, and enuresis. Enuresis was not related to any of the sleep behaviors assessed, and teeth grinding shared less than 9% of the variance with any of the other variables. Many of the variables loaded on more than one factor. The second factor, which was labeled bedtime resistance, was the only clearly unambiguous factor. Of the five factors that emerged, the third reflected positive affect, the fourth was a motor factor, and the fifth was an anxiety factor. Nightmares loaded on the anxiety factor as well as the first factor. The results of the study offered no support for the category of Disorders of Initiating and Maintaining sleep (DIMS), which has a childhood onset.This research was supported by a grant from the University of New Brunswick Research Fund.     

Eye movements while reading and searching spatially transformed text: A developmental examination

The effects of spatial manipulation on eye movement when subjects either read or searched through paragraphs were examined. Adults, third, and fifth graders were presented with paragraphs which were typed normally or in alternating case (upper and lower). The spacing between the words was either normal, filled, or absent. The results show that approximately twice as many character spaces are processed during search as during reading. Subjects made more fixations of shorter duration during search than reading. The data indicated that the ability to vary the size of the perceptual unit develops with experience. When spatial cues were unavailable, all subjects resorted to a letter-by-letter-like processing strategy in reading but not in search. Although reading and search were found to be sensitive to the same types of spatial manipulations, discrepancies of span and speed suggest qualitative differences; comprehension demands during reading can account for these differences. The data were interpreted to provide support for the two-stage model of Hochberg (1970).     

Efferent factors in natural event perception can be rationalized and verified: a reply to Turvey and Solomon

Contrary to the view that ambient light information unequivocally specifies phenomenal events, recent research suggests that natural event perception is determined by processes that pick up and combine visual and motor information. This thesis is challenged by Turvey and Solomon (1984). The present article responds to their misgivings by elaborating empirical methods and theoretical arguments of past work. A control experiment is also presented on pointing measurements of distance illusions related to esophoric shifts of eye convergence that are induced by near work. The soundness of both the empirical methodology and the theoretical arguments in support of the original thesis is upheld.     

A possible artifact in serial response behaviour

Using 12 subjects who worked for 12 min on a self-paced 5-choice serial response task, it was hypothesised that external events inserted by computer program in accordance with a random sequence of time intervals would bisect a greater proportion of long response times, and thus that the parameters of the resulting distributing would be greater than the parameters of the parent distribution or of a distribution in which responses were selected at random. The results confirmed the hypothesis and it was concluded that the Waiting Time Paradox as described by Feller (1966), is applicable to situations involving serial response tasks.