Pulling out all the stops to make the distance: Effects of effort and optical information in distance perception responses made by rope pulling.

Human observers perceive distance in remarkably stable and consistent manner across response methods and experimental paradigms. Most empirical work on the problem focused exclusively on geometrical variables, such as angle of declination below the horizon (Ooi, Wu, & He, 2001), with more recent considerations of nonvisual factors, such as effort (Proffitt, 2006). Hajnal, Bunch, and Kelty-Stephen (2014) showed that in addition to the object's physical angle of declination below the horizon, nonvisual variables related to effort were utilized when making distance estimates to objects placed on a sloped ramp. In that experiment, the horizontal ground surface was visible in the background when viewing objects placed on the sloped surface. To further investigate the joint utility of geometric and effort-based variables, we tested the effect of both classes of predictors on a natural hillside where a flat, horizontal surface was not visible in the background. This setup allowed us to evaluate whether observers rely on the same information to perceive distance on ramps versus real hills. The present research implicates the hypothesis that perceived effort and the geometry of space determine distance perception through interactions across multiple temporal scales of perceptual competence.

Going for distance and going for speed: effort and optical variables shape information for distance perception from observation to response.

Visually guided distance perception reflects a relationship of geometrical optical variables with the effort required when traversing the distance. We probed how the representations encoding optical variables might define this relationship. Participants visually judged distances on sloped surfaces and reproduced these distances over flat terrain by walking while blindfolded. We examined the responses for the effects of optical variables (i.e., angular declinations from eye height) and tested whether four measures of trial-by-trial effort moderated the use of the represented optical variables. We predicted that observation time and response speed relative to the observed distance would accentuate the effects of encoded optical variables, and that response time and response speed relative to the traversed distance would reduce the effects of those variables. The results confirmed all of the effects except those of observation time. Given the benefits of longer study for strengthening a memory trace, the failure of observation time to predict the use of optical variables raises questions about the representational encoding of visual traces for distance perception. Relationships among optical variables and other effort measures implicate the interaction of processes across multiple time scales, as in cascade dynamics. Cascade dynamics may provide new directions for accounts of visually guided distance perception.

Multiple measures of laterality in Garnett's bushbaby (Otolemur garnettii).

Behavioral laterality, a common measure of hemispheric specialization of the brain, has been examined in multiple tasks across several species of prosimian primates; however, there is inconsistency among findings between and within species that leaves many questions about laterality unanswered. Most studies have employed few measures of laterality, most commonly handedness. This study examined multiple measures of laterality within subjects in 17 captive-born Garnett's bushbabies (Otolemur garnettii) to assess the consistency of lateralized behaviors and to examine possible influences such as age, posture, novelty, and arousal to elucidate the relations between direction and strength of laterality. We measured reaching, turning bias, scent marking, tail wrapping, leading foot, side-of-mouth preference, and hand use in prey capture. Because autonomic arousal has been invoked as a determinant of strength of lateralization, we included multiple tasks that would allow us to test this hypothesis. All subjects were significantly lateralized on simple reaching tasks (P<0.01) and tail wrapping (P<0.01). Moreover, the number of animals lateralized on turning (P<0.01), leading limb (P<0.05), mouth use (P<0.01), and prey capture (P<0.01) was greater than would be expected by chance alone. There was consistency in the strength and direction of hand biases across different postures. Tasks requiring hand use were more strongly lateralized than tasks not involving hand use (P<0.001). The data do not support the assumption that arousal (as subjectively categorized) or novelty strengthens lateralized responding. The results of this study are discussed in terms of the effects of arousal, posture, and age on lateralized behavior.