Letting go: How the disappearance of a fixation target prompts the brain to shift attention
41.11, Monday, 18-May, 8:15 am - 9:45 am, Talk Room 1
Louisa Kulke1, Janette Atkinson1,2, Oliver Braddick2; 1Dept of Developmental Science, University College London, London, UK, 2Dept of Experimental Psychology, University of Oxford, Oxford, UK
A peripheral target can either be fixated when the current central target disappears (‘non-competition’) or while the central target remains visible (‘competition’) in the Fixation Shift Paradigm, where saccadic latencies can be used as a measure of shifts of attention. Competition, which leads to much slower saccadic latencies in young infants, requires disengagement from the current target, a process which is believed to depend on descending cortical input to oculomotor systems and is diagnostic of cerebral developmental problems (review: Atkinson and Braddick, Dev Med Child Neurol, 2012). We have recorded high density ERPs during the pre-saccadic interval, along with concurrent eye tracking, in both competition and non-competition from 38 normal adults. The adults showed small but significant advantages in saccadic latency for the non-competition condition. Patterns of ERP signals across the scalp, representing the processes of disengagement, attentional shift, and saccade preparation, were compared to investigate the cerebral basis of this advantage. A very early frontoparietal response, contralateral to the target, is seen in both conditions, as is a later, ipsilateral occipitoparietal response. When the contribution of the VEP to central target offset is allowed for, the latency of ERP responses for competition and non-competition is similar. However, both anterior and posterior responses show higher amplitudes in the non-competition than competition condition. These results will be discussed in terms of possible inhibitory connections between frontal, posterior, and subcortical oculomotor systems which may underlie the disengagement process. We are currently testing whether the ERP responses, characteristic of this network, provide developmental signatures of the disengagement process in infants, and potentially may serve as diagnostic signatures of the neural processes which impair fixation shifts in many developmental disorders (e.g. Braddick et al, Nature, 1992; Atkinson et al, Prog. Brain Res., 2011).