The development and predictive relations of play and language across the second year.

The play and language development of 171 toddlers was examined at 14 and 18 months by observing their activities on the Symbolic Play Test and by assessing their language skills using the MacArthur Communicative Development Inventories (MCDI) and the Reynell Developmental Language Scales. Additionally, data from the Bayley Scales of Infant Development and the MCDI were obtained at 24 months, in order to investigate how play and language measures taken at 14 and 18 months predict children's development at the age of 2 years. The results showed that the vocabulary production and symbolic play of the 14-month-old toddlers made a unique contribution to their language and cognitive skills at the age of 2 years, while at 18 months only language variables made a similar contribution. Other-directed pretense discriminated between the children's subsequent language and cognitive skills best, whereas nonsymbolic play had no independent predictive contribution. Significant gender differences were found in the use of nonsymbolic and symbolic play acts already at 14 months. Gender did not, however, contribute to the prediction of the children's subsequent skills, whereas maternal education significantly added to the prediction of the 2-year-olds' maximum sentence length and that of their cognitive development.     

Exocentric pointing in three-dimensional space

A study is reported of an exocentric pointing task in all three dimensions, in near space, with only two visible luminous objects--a pointer and a target. The task of the subject was to aim a pointer at a target. The results clearly show that visual space is not isotropic, since every set direction appeared to consist of two independent components--one in the projection onto a frontoparallel plane (tilt), the other in depth (slant). The tilt component shows a general trend across subjects, an oblique effect, and can be judged monocularly. The slant component is symmetrical in the mid-sagittal plane, requires the use of binocular information, and shows considerable differences between subjects. These differences seem to depend on the amount of binocular information used by each subject. There was a remarkably high level of consistency in the exocentric pointing, despite the absence of environmental cues. The within-subject consistency in the settings of the pointer corresponds to a consistency of about 1 min of arc in disparity of its tip, even though the pointer and target are separated by more than 5 deg.     

Sex differences in cognition: the role of testosterone and sexual orientation

The performance of both heterosexual and homosexual males and females was compared on four cognitive tasks which have been shown to reveal evidence of sexual dimorphism. In one spatial and one verbal task, significant sex and orientation effects were found. Significant relationships were also found between salivary free-testosterone levels and performance on both spatial tasks, but no significant associations were found for performance on the two verbal tasks. The present study revealed both within- and between-sex differences in cognition and indicates that these differences may be partly accounted for by the activational effects of free testosterone.     

Spacing effects on the memory for faces

25 undergraduate women studied 12 stimulus pictures of female faces successively presented in spaced or massed conditions and made affective judgments for the pictures along a dimension of like to dislike. One week after the exposure (study) period, subjects were given an identification test comprised of photographs of the same female faces with different expressions. Analysis showed that the pictures presented in the spaced condition were more frequently and accurately identified than those presented under the massed condition and that affective judgment was unrelated to conditions of presentation.     

Ecological relevance of stereopsis in one-handed ball-catching

The aim of this study was to compare one-handed catching performance between catchers with high (n = 10) and low (n = 10) binocular depth vision or stereopsis. In two sessions of 90 trials, tennis balls were projected at three different velocities towards the subject's shoulder region. Participants with good stereopsis were more successful, although the difference in number of correct catches fell short of significance. More specifically, catchers with low stereopsis made more temporal errors, but no differences in spatial errors. As the velocity of the ball increased, the initiation of the catch was delayed and catching performance decreased. The finding that stereopsis affected timing of the catch challenges the 'monocular tau hypothesis' in the control of interceptive timing, while the velocity effect shows that the act of catching a ball is not initiated at a constant time-to-contact.     

Diurnal pattern of luminance discrimination in humans

The visual discrimination threshold can be considered as an image of the resolution power of the visual system. Measured with a psychophysical method, it shows a diurnal pattern with a low threshold in the morning, i.e., high sensitivity and an increase in the afternoon that persists until the early evening.     

Effects of practice and task constraints on stiffness and friction functions in biological movements

A dynamical model of the movements of the platform of a ski-simulator was derived from experimental data, using the graphical and statistical methods developed by Beek and Beek (Beek, P. J., & Beek, W. J. (1988). Human Movement Science, 7, 301–342). The data were collected in an experiment in which both amplitude and practice were manipulated. The data were filtered and further reduced to normalised cycles that were averaged within and across subjects. Graphical methods were applied to these averaged normalised cycles to determine the stiffness and friction terms to be included in the model. The relative contribution of each term was assessed by means of multiple regression. The model, which included cubic and quintic Duffing terms and one or two dissipative Van der Pol terms, accounted on average for 99.2% of the variance. The exact parameter setting of the model differed considerably across subjects. For one subject, a qualitatively different model, including Rayleigh instead of Van der Pol terms, provided a better account of the data. Systematic changes of the coefficients in the model, related to amplitude and the duration of practice, were evident.     

Age-related deficits in generation and manipulation of mental images: I. The role of sensorimotor speed and working memory.

The authors investigated age-related slowing of information processing in mental imagery tasks. Eighty-five healthy adults (ages 18 to 77) performed a visual, sensorimotor, reaction-time task; a visual-perceptual choice reaction task; and 3 mental imagery tasks that varied in apparent difficulty and involved stimuli at 2 levels of graphic complexity. Age was associated with prolongation of response time across all tasks and both levels of stimulus complexity. Accuracy of response was adversely affected by increase in stimulus complexity in all tasks, whereas it was negatively related to age only on the tasks with substantial mental imagery requirements. Slowing of information processing and reduction in accuracy were mediated by declines in working memory but not by decrease of sensorimotor speed.     

The attentional demands of encoding and retrieval in younger and older adults: 2. Evidence from secondary task reaction time distributions

Three studies examined the effects of encoding or retrieval on properties of secondary task reaction time (RT) distributions in younger and older adults. Relative to full attention conditions, encoding and retrieval increased secondary task RT medians and standard deviations more for older adults than for younger adults, and the age-related RT increase was most pronounced among the slowest RTs. Hierarchical regression analyses revealed two age-related mechanisms underlying these effects, which were interpreted as cognitive slowing and reductions in attentional resources. Cognitive slowing affects the entire RT distribution regardless of the memory task. By contrast, reduced attentional resources result in very long RTs, especially when the tasks require self-initiated encoding or retrieval operations.