What visual information do we use to guide movement through our environment? Self-movement produces a pattern of motion on the retina, called optic flow. During translation, the direction of movement (locomotor direction) is specified by the point in the flow field from which the motion vectors radiate - the focus of expansion (FoE) [1-3]. If an eye movement is made, however, the FoE no longer specifies locomotor direction [4], but the 'heading' direction can still be judged accurately [5]. Models have been proposed that remove confounding rotational motion due to eye movements by decomposing the retinal flow into its separable translational and rotational components ([6-7] are early examples). An alternative theory is based upon the use of invariants in the retinal flow field [8]. The assumption underpinning all these models (see also [9-11]), and associated psychophysical [5,12,13] and neurophysiological studies [14-16], is that locomotive heading is guided by optic flow. In this paper we challenge that assumption for the control of direction of locomotion on foot. Here we have explored the role of perceived location by recording the walking trajectories of people wearing displacing prism glasses. The results suggest that perceived location, rather than optic or retinal flow, is the predominant cue that guides locomotion on foot.

Background: In order to obtain a measure of nutrient intake, a measure or estimate of the amount of food consumed is required. Weighing foods imposes a large burden on subjects, often resulting in underreporting. Tools are available to assist subjects in providing an estimate of portion size and these include food photographs. The application of these tools in improving portion size estimation by children has not been investigated systematically. Objectives: To assess the accuracy with which children are able to estimate food portion sizes using food photographs designed for use with adults, and to determine whether the accuracy of estimates is improved when age-appropriate portion size photographs are provided. Design: Original data from three separate studies, on the accuracy of portion size estimates by adults using food photographs, by children using adult photographs and by children using age-appropriate photographs, are analysed and compared. Subjects: One hundred and thirty-five adults aged 18 to 90 years and 210 children aged 4 to 11 years. Results: Children's estimates of portion sizes using age-appropriate food photographs were significantly more accurate (an underestimate of 1% on average) than estimates using photographs designed for use with adults (an overestimate of 45% on average). Accuracy of children's estimates of portion size using age-appropriate photographs was not significantly different from that of adults. Children overestimated a food's weight by 18% on average and adults underestimated by 5%. Conclusions: Providing children with food photographs depicting age-appropriate portion sizes greatly increases the accuracy of portion size estimates compared with estimates using photographs designed for use with adults.

A number of methods have been developed to assist subjects in providing an estimate of portion size but their application in improving portion size estimation by children has not been investigated systematically. The aim was to develop portion size assessment tools for use with children and to assess the accuracy of children's estimates of portion size using the tools. The tools were food photographs, food models and an interactive portion size assessment system (IPSAS). Children (n 201), aged 4-16 years, were supplied with known quantities of food to eat, in school. Food leftovers were weighed. Children estimated the amount of each food using each tool, 24 h after consuming the food. The age-specific portion sizes represented were based on portion sizes consumed by children in a national survey. Significant differences were found between the accuracy of estimates using the three tools. Children of all ages performed well using the IPSAS and food photographs. The accuracy and precision of estimates made using the food models were poor. For all tools, estimates of the amount of food served were more accurate than estimates of the amount consumed. Issues relating to reporting of foods left over which impact on estimates of the amounts of foods actually consumed require further study. The IPSAS has shown potential for assessment of dietary intake with children. Before practical application in assessment of dietary intake of children the tool would need to be expanded to cover a wider range of foods and to be validated in a 'real-life' situation.Portion size estimation: Food photographs: Interactive portion size assessment system: ChildrenTo monitor the diet of populations there is a need for methods that are accurate, easy for the subject to complete and appropriate to the target population.Assessing habitual food intake of any population group is challenging. Common problems encountered include underreporting 1,2 , subject selection bias and recording bias 3 . Additional limitations must be considered when children are the subjects. The skills and limitations of the population to be studied must be considered. When children are the subjects these may include issues of literacy and writing skills, limited food recognition skills, memory constraints and concentration span.In order that intakes of food can be converted into intakes of nutrients or other food constituents, a measure or estimate of the portion size of each food item consumed is required. Weighing and recording all foods eaten requires a highly motivated and committed subject population that is unlikely to be representative of the general population. Berg et al. discuss that when participation in a project requires a great deal of subject commitment or divulging information of a sensitive nature then there is a risk that the response rate will be low 4 . Of those approached to take part, 64 % completed the recent National Diet and Nutrition Survey (NDNS) of young people aged 4-18 years in the UK, which used a 7 d weighed diary method 5 . In addition, ap...

The shirt colour worn by sportsmen can affect the behaviour of the competitors, but Hill and Barton show that it may also influence the outcome of contests. By analysing the results of men's combat sports from the Athens 2004 Olympics, they found that more matches were won by fighters wearing red outfits than by those wearing blue; they suggest that red might confer success because it is a sign of dominance in many animal species and could signal aggression in human contests. Here we use another data set from the 2004 Olympics to show that similar winning biases occur in contests in which neither contestant wears red, indicating that a different mechanism may be responsible for these effects.

Although it is well known that motion-in-depth can be detected using binocular cues, it is not known whether those cues can be used to judge the speed of an object moving in depth. There are at least two possible binocular cues that could be used by the visual system to calculate three dimensional (3-D) speed: the rate of change of binocular disparity, or a comparison of the speeds of motion in the two eyes. We tested which of these cues is used to discriminate the speed of motion-in-depth. First, speed discrimination was measured for a dot moving away from the observer in depth (along the z-axis) and for a random dot stereogram in which a central square moved away from the observer in depth. These stimuli contained both disparity and monocular motion cues. Speed discrimination thresholds were as good for 3-D motion as for monocular sideways motion. Second, a dynamic random dot stereogram (in which the random dot pattern was replaced by a new dot pattern every frame) was used to remove consistent monocular cues. 3-D speed discrimination was now very poor, suggesting that the rate of change of disparity is not a good cue for 3-D speed. Finally, we tested whether observers were able to use the monocular motion cue from one eye to perform the speed discrimination task, or whether there had to be a comparison of the two eyes' monocular cues. By adding a small x-axis velocity component (with random direction) to the z-axis motion, it was possible to disrupt the monocular motion signals without altering the speed of the motion in 3-D. This manipulation did not disrupt the observers' performance, suggesting that monocular speed cues were not being used independently but that there was a comparison of monocular motion signals from the two eyes.