Interactions between visual and semantic processing during object recognition revealed by modulatory effects of age of acquisition

Abstract

The age of acquisition (AoA) of objects and their names is a powerful determinant of processing speed in adulthood, with early-acquired objects being recognized and named faster than late-acquired objects. Previous research using fMRI (Ellis et al., 2006. Traces of vocabulary acquisition in the brain: evidence from covert object naming. NeuroImage 33, 958–968) found that AoA modulated the strength of BOLD responses in both occipital and left anterior temporal cortex during object naming. We used magnetoencephalography (MEG) to explore in more detail the nature of the influence of AoA on activity in those two regions. Covert object naming recruited a network within the left hemisphere that is familiar from previous research, including visual, left occipito-temporal, anterior temporal and inferior frontal regions. Region of interest (ROI) analyses found that occipital cortex generated a rapid evoked response (~75–200ms at 0–40Hz) that peaked at 95ms but was not modulated by AoA. That response was followed by a complex of later occipital responses that extended from ~300 to 850ms and were stronger to early- than late-acquired items from ~325 to 675ms at 10–20Hz in the induced rather than the evoked component. Left anterior temporal cortex showed an evoked response that occurred significantly later than the first occipital response (~100–400ms at 0–10Hz with a peak at 191ms) and was stronger to early- than late-acquired items from ~100 to 300ms at 2–12Hz. A later anterior temporal response from ~550 to 1050ms at 5–20Hz was not modulated by AoA. The results indicate that the initial analysis of object forms in visual cortex is not influenced by AoA. A fastforward sweep of activation from occipital and left anterior temporal cortex then results in stronger activation of semantic representations for early- than late-acquired objects. Top-down re-activation of occipital cortex by semantic representations is then greater for early than late acquired objects resulting in delayed modulation of the visual response.