Abstract
Given the dynamic nature of our external world, the ability to accurately judge rapidly appearing and disappearing objects is critical. Previous research has shown that adults are able to individuate two alternating states at a temporal rate of up to 7–10 Hz (Verstraten et al., 2000; Battelli et al., 2003; Aghdaee and Cavanagh, 2007), termed the Gestalt flicker fusion rate (van de Grind et al., 1973). This limit has been linked to the temporal resolution of attention where individuation of the states is mediated by visual attention. The aim of this study was to determine the temporal limit of attention in 6- to 15-month-old infants by psychophysically measuring phase discrimination.
Stimuli were four squares, flickering between black and white states at one of four temporal frequencies (0.1, 2, 5, or 8 Hz), for 5 seconds. The target square, randomly determined, flickered 180° out-of-phase from the other three squares. Only if infants can individuate the states of the squares will they be able to detect and prefer the target. Eye tracking data was used to calculate a target-preference score for each trial (duration of looking to target divided by total duration of on-screen looking). The criterion for reliable target discrimination was an average target-preference score greater than chance (0.25). Results revealed that infants across all ages discriminated the target only at a temporal frequency of 0.1 Hz (t(34) = 5.334, p = 0.0001), suggesting that the resolution of temporal attention in infants is much coarser than adults. Based on evidence that patients who are affected by right parietal lesions present with dramatically lower temporal frequency limits, this finding may shed light on development of the function of right parietal areas. Future experiments will seek to pinpoint infants' thresholds by examining performance at temporal frequencies between 0.1 and 2 Hz.