Walking in an environment of moving ground texture

The visual control of global body movements has mainly been studied in terms of the maintenance of balance. The present experiment examined the effect of moving visual surroundings on the speed of locomotion. A virtually boundless optical environment was generated by the projection of a dotted texture on the ground that was reflected on large vertical mirrors fixed along the walls of the room. Subjects' head velocity was recorded over a walking path of about 10 m along the projection surface. In the experimental sessions, the texture was animated and moved at different speeds in the same direction as the subject or in the opposite direction. In the control condition, the projected texture remained motionless and therefore appeared to pass by at the subjects' walking speed. The subjects' task was to maintain a constant walking speed as far as possible over the different conditions. Changes in walking speed give indications of how the processing of optical flow modulates locomotor activity.     

Further explorations of common-sense representations of common illnesses

A simple method is presented for measuring people's illness cognitions--their common-sense representations of common illnesses. Data were collected from 1,628 different respondents who described a recent illness form 1 to 3 separate times over a 17-month period. A free-clustering task performed by a set of naive participants confirmed that these cognitions fall into the five components that have been previously noted: identity, time line, consequences, cause, and cure. These five components are found to be reasonably stable over time and across different illness episodes. Several consequences of these illness cognitions, in terms of changes in health-locus-of-control beliefs and different propensities to visit a doctor, are also noted. Specifically, controllable attributions for getting sick and personal responsibility attributions for getting better are associated with increased beliefs in Self-Control Over Health and decreased beliefs in Chance Health Outcomes; people with strong Identity and Cure components in their common-sense representations of common illnesses have a greater propensity to visit a doctor when feeling ill.     

Territorial prior residence,size asymmetry,and escalation of aggression in convict cichlids (Cichlasoma nigrofasciatum Günther)

The present study was designed to assess the effects of resident versus intruder size differences upon the territorial prior-residence effect and level of territorial aggression in convict cichlids. Prior to a direct territorial dominance encounter, pairs of fish were randomly composed for one of three experimental treatment conditions: 1) the resident having a body-length 20–30% larger than that of the intruder, 2) the intruder having a body-length 20–30% larger than the resident, or 3) the combatants' body-lengths differing by no more than 5%. After a 3-day territorial acclimation period in their individual territories, the subject designated as the intruder was introduced to the resident's territory. For each encounter the pairmember that attacked first and the one that ultimately established dominance were recorded. Also measured during the encounter were the total number of bites, resident bites, intruder bites, and jaw-locking frequency and duration. The results revealed that there was a significant resident advantage in the resident-larger group. The intruder-larger group resulted in a significant intruder dominance advantage. However, no significant dominance advantage occurred in the same-size group. As predicted by game theory, there was significantly less escalation of aggression in contests in which one combatant held both designated asymmetric cues (prior residence, size) than in contests in which one combatant had prior residence, or when these two asymmetric cues were divided between the pairmembers. The size asymmetry is more important in determining dominance than the prior-residence asymmetry, for the particular size-difference range selected in the present study.