Spatial Attention-Modulated Surround Suppression Across Development: A Psychophysical Study
Wong Kee You, Audrey Marie Beatrice
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Several studies have demonstrated that surrounding a given spatial location of attentional focus is a suppressive field (e.g., Hopf et al., 2006). Though several studies have provided psychophysical (e.g., Cutzu & Tsotsos, 2003) and neural evidence of this effect in young adults (e.g., Boehler et al., 2009), whether this phenomenon is also observed in development was not fully known. Experiment 1 of the current study was therefore conducted to examine whether attention-modulated surround suppression was observed in younger age groups. Participants between the ages of 8 and 22 years were tested on a two-alternative forced choice task, in which their accuracy in discriminating between two red target letters among black distractor letters was measured. A spatial cue guided the participants attention to the upcoming location of one of the target letters. As would be predicted for the young adults, their accuracy increased as the inter-target separation increased, suggesting that visual processing is suppressed in the immediate vicinity of an attended location. Pre-adolescents (12 to 13 years) and adolescents (14 to 17 years) also exhibited attentional surround suppression, but intriguingly their inhibitory surround appeared to be larger than that of young adults. The 8- to 11-year-olds did not exhibit attentional suppression. In Experiment 2, when a central cue instead of a spatial cue was presented, surround suppression was no longer observed in an independent set of 8- to 27-year-olds, suggesting that the findings of Experiment 1 were indeed related to spatial attention. In Experiment 3, yet another independent group of 8- to 9-year-olds were tested on a modified version of the Experiment 1 task, where the cue presentation time was doubled to provide them with more support and more time to complete their top-down feedback processes. With this manipulation, attention-modulated surround suppression was still not observed in the 8- to 11-year-olds. Overall the current study findings suggest that top-down attentional feedback processes are still immature until approximately 12 years of age, and that they continue to be refined throughout adolescence. Protracted white matter maturation and diffuse functional connectivity in younger age groups are some of the potential underlying mechanisms driving the current findings.