Averaging, not internal noise, limits the development of coherent motion processing.
Bottom Line: To this end, we presented equivalent noise direction discrimination tasks and motion coherence tasks at both slow (1.5°/s) and fast (6°/s) speeds to children aged 5, 7, 9 and 11 years, and adults.We show that, as children get older, their levels of internal noise reduce, and they are able to average across more local motion estimates.Our results suggest that the development of coherent motion sensitivity is primarily limited by developmental changes within brain regions involved in integrating motion signals (e.g., MT/V5).
Affiliation: Centre for Research in Autism and Education (CRAE), Institute of Education, University of London, 55-59 Gordon Square, Institute of Education, London WC1H 0NU, UK. Electronic address: email@example.com.Show MeSH
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Mentions: The traditional motion coherence paradigm cannot distinguish between local and global limits to motion perception and has hence obscured our understanding of what limits global motion processing during development (and in a variety of neurodevelopmental disorders; Dakin and Frith, 2005). To address this issue, the current study used the equivalent noise paradigm (Barlow, 1956; Pelli, 1990) to determine whether local or global processing limits motion coherence sensitivity in development. The equivalent noise paradigm is based on comparing human performance to that of an ideal observer that is limited both by additive internal noise and by how completely it samples the information available from the stimulus (Pelli, 1990). When equivalent noise analysis is applied to direction discrimination (Dakin et al., 2005), internal noise maps onto the precision with which individual motion directions are estimated and sampling represents an estimate of the effective number of local motion directions that are globally pooled (or averaged). Whereas motion coherence stimuli contain both signal dots and randomly moving noise dots, equivalent noise stimuli contain dots whose directions (on any one trial) are sampled from a single Gaussian distribution (Dakin et al., 2005). The standard deviation of this distribution is varied across conditions, in order to manipulate the level of stimulus variability (or ‘external noise’; see Fig. 1A).
Affiliation: Centre for Research in Autism and Education (CRAE), Institute of Education, University of London, 55-59 Gordon Square, Institute of Education, London WC1H 0NU, UK. Electronic address: firstname.lastname@example.org.