Springer Science and Business Media LLC

We investigated the effect of systematically varying the phase relationship between 0.5-Hz sinusoidal z-axis optokinetic (OKN) and linear acceleration stimuli upon the resulting vertical eye movement responses of five humans. Subjects lay supine on a linear sled which accelerated them sinusoidally along their z-axis at 0.4 g peak acceleration (peak velocity 1.25 m/s). A high-contrast, striped z-axis OKN stimulus moving sinusoidally at 0.5 Hz, 70°/s peak velocity was presented either concurrently or with the acceleration stimulus or alone. Subjects' vertical eye movements were recorded using scleral search coils. When stimuli were paired in the naturally occurring relationship (e.g., visual stripes moving upward paired with downward physical acceleration), the response was enhanced over the response to the visual stimulus presented alone. When the stimuli were opposed (e.g., visual stripes moving upward during upward physical acceleration, a combination that does not occur naturally), the response was not significantly different from the response to the visual stimulus presented alone. Enhancement was maximized when the velocities of the visual and motion stimuli were in their normal phase relationship, while the response took intermediate values for other phase relationships. The phase of the response depended upon the phase difference between the two inputs. We suggest that linear self-motion processing looks at agreement between the two stimuli — a sensory conflict model.

Many daily activities require separate tasks of the arms and legs to be performed together, as in driving where one foot controls the accelerator, one arm steers, and the other arm and foot shift gears and clutch. Strategies and underlying mechanisms for attention allocation and task prioritization have been explored in standing and walking while performing a manual or cognitive task. These studies reveal a task-related strategy that often, but not always, prioritizes the lower limb task of walking. However, in the absence of locomotion and gait-related postural control, as in sitting, multi-limb dual-task strategies are largely unexplored. Therefore, to characterize dual-task interference of arm and leg tasks during a driving-like activity, seated participants were assessed for the interference effect on hand velocity and movement time of a three-phase reach task and on the error in tracking of a foot-pedal ramp-tracking task. We found that the dual-task cost to reaching shown as decreases in reach performance differed among the three phases, that the cost to foot-pedal tracking also differed by phase, and that the between-task trade-off and prioritization strategy varied between the steep and gradual tracking ramps. Therefore, we propose that attention to concurrent reaching and foot-pedal tracking was flexibly allocated based on phase of the tasks.

Corporeal awareness is a difficult concept which refers to perception, knowledge and evaluation of one’s own body as well as of other bodies. We discuss here some controversies regarding the significance of the concepts of body schema and body image, as variously entertained by different authors, for the understanding of corporeal awareness, and consider some newly proposed alternatives. We describe some recent discoveries of cortical areas specialized for the processing of bodily forms and bodily actions, as revealed by neuroimaging, neurophysiological, and lesion studies. We further describe new empirical and theoretical evidence for the importance of interoception, in addition to exteroception and proprioception, for corporeal awareness, and discuss how itch, a typical interoceptive input, has been wrongly excluded from the classic concept of the proprioceptive–tactile body schema. Finally, we consider the role of the insular cortex as the terminal cortical station of interoception and other bodily signals, along with Craig’s proposal that the human insular cortex sets our species apart from other species by supporting consciousness of the body and the self. We conclude that corporeal awareness depends on the spatiotemporally distributed activity of many bodies in the brain, none of which is isomorphic with the actual body.

The organisation of the thalamofugal visual projections to the forebrain has been determined in chick embryos by injecting retrograde tracers (true blue and either fluorogold or diamidino yellow) into the left or right hyperstriatum. The embryos were injected on day 19 of incubation and allowed to survive for a further 4 days. Unlike chicks posthatching, the embryos were found to have no asymmetry of the thalamofugal visual projections, irrespective of whether they had received 24 h of light exposure prior to injecting the tracer dyes or had been kept in darkness. The light exposure did, however, lead to a significant increase in the ratio of the number of cell bodies in the thalamus labelled contralaterally to the injection site to the number labelled ipsilaterally (CI ratio) in male embryos. The elevation of the CI ratio appeared to be due to an increase in the number of contralateral projections from each side of the thalamus to the hyperstriatum on the other side of the forebrain. Thus, growth of these visual projections is promoted by light experience during the later stages of embryonic development. Most likely, light stimulation promotes increased arborisation of end-terminals in the hyperstriatum. Development of the thalamofugal visual projections in female embryos was not influenced by exposure to light, a finding consistent with earlier studies demonstrating that circulating oestrogen either inhibits or over-rides the sensitivity of these developing neurones to light stimulation.

The aim of this study was to examine the development of underlying motor control strategies in young children by characterizing the changes in performance of a visually guided force regulation task using two different grip formations; a whole-hand power grip (developmentally easier) and a thumb-index finger precision grip (developmentally more advanced). Typically developing preschool children (n=50, 3.0–5.5 years) used precision and power grips to perform a ramp and hold task with their dominant and non-dominant hands. Participants performed five trials with each hand and grip holding the force at 30% of their maximum volitional contraction for 3 s. The data were examined for both age-related and performance-related changes in motor performance. Across ages, children increased in strength, decreased in initial overshoot of the target force level, and decreased in rate of force release. Results of a cluster analysis suggest non-linear changes in the development of force control in preschool children, with a plateau in (or maturation of) velocity measures (rate of force increase and force decrease) earlier than in amplitude-related measures (initial force overshoot and force variability).

The representation of magnitude information enables humans and animal species alike to successfully interact with the external environment. However, how various types of magnitudes are processed by single neurons to guide goal-directed behavior remains elusive. Here, we recorded single-cell activity from the dorsolateral prefrontal (PFC), dorsal premotor (PMd) and cingulate motor (CMA) cortices in monkeys discriminating discrete numerical (numerosity), continuous spatial (line length) and basic sensory (spatial frequency) stimuli. We found that almost exclusively PFC neurons represented the different magnitude types during sample presentation and working memory periods. The frequency of magnitude-selective cells in PMd and CMA did not exceed chance level. The proportion of PFC neurons selectively tuned to each of the three magnitude types were comparable. Magnitude coding was mainly dissociated at the single-neuron level, with individual neurons representing only one of the three tested magnitude types. Neuronal magnitude discriminability, coding strength and temporal evolution were comparable between magnitude types encoded by PFC neuron populations. Our data highlight the importance of PFC neurons in representing various magnitude categories. Such magnitude representations are based on largely distributed coding by single neurons that are anatomically intermingled within the same cortical area.