Abstract
Visual perceptual learning (VPL) is defined as a long-term performance change on a visual task resulting from visual experience or training. After such training ends, VPL is fragile and needs to be stabilized against being retrogradely interfered with by new stimuli or tasks. Although stabilization is a well-established mechanism in VPL and other types of learning, it is unclear whether it changes across the life span. Here, we investigated how mechanisms that stabilize VPL change from childhood to adulthood. Participants (n = 13 children, 8-11 years old, and n = 14 adults, 18-29 years old) were trained on a two-interval forced choice orientation detection task with two different orientations in separate blocks. Between blocks participants rested for 60 min. VPL was measured as an improvement in detection performance for each trained orientation on a separate day. The results show that adults developed VPL only for the second trained orientation, indicating that VPL of the second trained orientation retrogradely interfered with stabilization of VPL of the first trained orientation. In contrast, children developed VPL for both trained orientations and did not show any interference, suggesting that post-training processing of VPL is significantly different between children and adults. We measured neurochemical mechanisms underlying the observed changes using magnetic resonance spectroscopy with new groups of participants (n = 13 children, 8-11 years old, n = 14 adults, 18-30 years old). We found that children after VPL training immediately exhibited increased concentrations of inhibitory neurotransmitter (GABA) over excitatory neurotransmitter (glutamate/glutamine) in visual cortex, whereas no such changes occurred in adults. These results suggest that children’s VPL is stabilized against interfering stimuli or tasks by inhibiting interfering mechanisms in visual cortex immediately after training ends. These dynamics do not occur in adulthood, which makes VPL in adults more susceptible to retrograde interference.