Comparing Locomotion With Lever-press Travel In An Operant Simulation Of Foraging

An operant model of foraging was studied. Rats searched for food by pressing on the left lever, the patch, which provided one, two, or eight reinforcers before extinction (i.e., zero reinforcers). Obtaining each reinforcer lowered the probability of receiving another reinforcer, simulating patch depletion. Rats traveled to another patch by pressing the right lever, which restored reinforcer availability to the left lever. Travel requirement changed by varying the probability of reset for presses on the right lever; in one condition, additional locomotion was required. That is, rats ran 260 cm from the left to the right lever, made one response on the right lever, and ran back to a fresh patch on the left lever. Another condition added three hurdles to the 260-cm path. The lever-pressing and simple locomotion conditions generated equivalent travel times. Adding the hurdles produced longer times in patches than did the lever-pressing and simple locomotion requirements. The results contradict some models of optimal foraging but are in keeping with McNair's (1982) optimal giving-up time model and add to the growing body of evidence that different environments may produce different foraging strategies.     

Resilient Adolescent Adjustment Among Girls: Buffers of Childhood Peer Rejection and Attention-Deficit/Hyperactivity Disorder

Examined a risk-resilience model of peer rejection and attention-deficit/hyperactivity disorder (ADHD) in a 5-year longitudinal study of 209 ethnically and socioeconomically diverse girls aged 6-13 at baseline and 11-18 at follow-up. Risk factors were childhood ADHD diagnosis and peer rejection; hypothesized protective factors were childhood measures of self-perceived scholastic competence, engagement in goal-directed play when alone, and popularity with adults. Adolescent criterion measures were multi-informant composites of externalizing and internalizing behavior plus indicators of academic achievement, eating pathology, and substance use. ADHD and peer rejection predicted risk for all criterion measures except for substance use, which was predicted by ADHD only. ADHD and peer rejection predicted lower adolescent academic achievement controlling for childhood achievement, but they did not predict adolescent externalizing and internalizing behavior after controlling for baseline levels of these constructs. Regarding buffers, self-perceived scholastic competence in childhood (with control of academic achievement) predicted resilient adolescent functioning. Contrary to hypothesis, goal-directed play in childhood was associated with poor adolescent outcomes. Buffers were not found to have differential effectiveness among girls with ADHD relative to comparison girls.     

Acute and chronic effects of cocaine on the spontaneous behavior of pigeons

The present experiment examined the effects of acute and daily cocaine on spontaneous behavior patterns of pigeons. After determining the acute effects of a range of doses, 9 pigeons were divided into three groups that received one of three doses of cocaine daily, either 1.0, 3.0, or 10.0 mg/kg cocaine. Measures were taken of spontaneous locomotion, pecking, preening, and emesis. Under daily administration, cocaine induced consistent and substantial enhancements of its locomotor effects in all 9 pigeons, consistent with the phenomenon of locomotor sensitization. The maximum locomotor output did not differ according to the size of the daily dose. Locomotion was not elevated following tests of the saline vehicle, suggesting the effect was due to cocaine, not to a change in baseline or reactivity to the injection procedure. Cocaine dose‐dependently decreased preening when given acutely, and those effects were not altered by repeated cocaine administration. Pecking occurred at very low rates and was unresponsive to cocaine treatment. Cocaine‐induced emesis showed a dose‐dependent increase under initial tests with cocaine, and those effects were attenuated following daily exposure. In a final condition, cocaine was replaced with daily saline for 30 days to assess the persistence cocaine‐related increases in locomotion. Approximately half of the pigeons continued to show enhanced effects even after 30 days without cocaine, so although persistence was obtained, it showed marked intersubject variability. The data indicate that the effects of repeated cocaine administration on the behavior of pigeons shows parallels with many effects commonly reported with rodents (i.e., increased locomotion following repeated treatment, decrease in preening or grooming, persistence following drug withdrawal).     

Coordination of Eye and Leg Movements During Visually Guided Stepping

In the present study, 2 related hypotheses were tested: first, that vision is used in a feedforward control mode during precision stepping onto visual targets and, second, that the oculomotor and locomotor control centers interact to produce coordinated eye and leg movements during that task. Participants' (N = 4) eye movements and step cycle transition events were monitored while they performed a task requiring precise foot placement at every step onto irregularly placed stepping stones under conditions in which the availability of visual information was either restricted or intermittently removed altogether. Accurate saccades, followed by accurate steps, to the next footfall target were almost always made even when the information had been invisible for as long as 500 ms. Despite delays in footlift caused by the temporary removal (and subsequent reinstatement) of visual information, the mean interval between the start of the eye movement and the start of the swing toward a target did not vary significantly (p > .05). In contrast, the mean interval between saccade onset away from a target and a foot landing on that target (stance onset) did vary significantly (p < .05) under the different experimental conditions. Those results support the stated hypotheses.     

Postural Requirements and Progression Velocity in Young Walkers

This article describes developmental changes in gait velocity and relates these changes to gait parameters that index postural stability (step width and lateral acceleration) and two components of velocity (cadence and step length).

Five children were observed longitudinally over a 2-year period after onset of independent walking. Their range of speed increased threefold in the first 6 months of independent walking and then remained constant. In contrast, step width decreased approximately twofold. Whereas in adults, cadence and step length contribute approximately equally to speed, when infants first begin to walk independently, increase in velocity is due mostly to increased step length. After 5 months of independent walking, the pattern reverses, and increase in velocity is due primarly to increased cadence. The pattern remains constant over the next 18 months. From a developmental point of view, the data lead us to interpret early walking (the first 5 months) as a process of integration of postural constraints into the dynamic necessities of gait movement. A second phase, beginning after 4 to 5 months of independent walking, is considered to be a tuning phase characterized by a more precise adjustment of the gait parameters.     

Discordance in Recovery Between Altered Locomotion and Muscle Atrophy Induced by Simulated Microgravity in Rats

Exposure to a microgravity environment leads to adverse effects in motion and musculoskeletal properties. However, few studies have investigated the recovery of altered locomotion and muscle atrophy simultaneously. The authors investigated altered locomotion in rats submitted to simulated microgravity by hindlimb unloading for 2 weeks. Motion deficits were characterized by hyperextension of the knees and ankle joints and forward-shifted limb motion. Furthermore, these locomotor deficits did not revert to their original form after a 2-week recovery period, although muscle atrophy in the hindlimbs had recovered, implying discordance in recovery between altered locomotion and muscle atrophy, and that other factors such as neural drives might control behavioral adaptations to microgravity.     

Explaining adolescents’ cigarette smoking: A comparison of four modes of action control and test of the role of self-regulatory mode

The present study compared how well four modes of action control (intentional, habitual, reactive and stereotype activation) explain adolescents’ cigarette smoking, and examined whether individual differences in self-regulation (locomotion and assessment tendencies; Higgins, Kruglanski, & Pierro, 2003 Higgins, ET, Kruglanski, AW and Pierro, A. 2003. Regulatory mode: Locomotion and assessment as distinct orientations. Advances in Experimental Social Psychology, 25: 293–344.  [Google Scholar]) moderate the behavioural impact of the respective modes. Findings from a prospective questionnaire survey showed that (a) willingness, prototype perceptions and past behaviour–but not intention–predicted smoking behaviour, and explained 63% of the variance, and (b) the assessment mode of self-regulation moderated the past behaviour–future behaviour relation such that past behaviour had less impact on future smoking behaviour at high levels of assessment. These findings suggest that adolescents’ smoking is controlled by stereotype activation, habitual and reactive processes. Implications of the results for designing effective adolescent smoking cessation programmes are considered.     

Load theory of selective attention and the role of perceptual load: Is it time for revision?

Perceptual load hypothesis is proposed as a compromise between early and late theory of selective attention which states that the selection will operate early when the load on perception is high and it will operate late when the load on perception is low. Experimental findings have shown that the perceptual load hypothesis is too simplistic in nature as perceptual load is not the only determinant of selection processes. It is difficult to apply the load hypothesis to explain the occurrence of early selection in low load displays as well as the selection processes that operate on distractor and target stimuli that are a part of the same object. Factors like spatial proximity, cues that manipulate the spatial extent of attentional focus, salience of targets as well as the distractors, and perceptual grouping between the target and the distractors should be taken into account while explaining the selective control of attention. Thus, the perceptual load of the display is one such factor that affects selective attention and goal-directed behaviour, but it is not the only factor to affect the selective control of attention.     

Mechanisms for regulating step length while running towards and over an obstacle

The ability to run across uneven terrain with continuous stable movement is critical to the safety and efficiency of a runner. Successful step-to-step stabilization while running may be mediated by minor adjustments to a few key parameters (e.g., leg stiffness, step length, foot strike pattern). However, it is not known to what degree runners in relatively natural settings (e.g., trails, paved road, curbs) use the same strategies across multiple steps. This study investigates how three readily measurable running parameters – step length, foot placement, and foot strike pattern – are adjusted in response to encountering a typical urban obstacle – a sidewalk curb. Thirteen subjects were video-recorded as they ran at self-selected slow and fast paces. Runners targeted a specific distance before the curb for foot placement, and lengthened their step over the curb (p < 0.0001) regardless of where the step over the curb was initiated. These strategies of adaptive locomotion disrupt step cycles temporarily, and may increase locomotor cost and muscle loading, but in the end assure dynamic stability and minimize the risk of injury over the duration of a run.