fMRI RESULTS

1. SUMMARY It is well known that orienting attention to a particular perceptual feature of an item, such as its location, can facilitate its detection or recognition. It is not clear whether attentional orienting to non-perceptual stimulus attributes can also enhance behaviour. We investigated this question by probing whether it is possible to orient attention to semantic categories of verbal stimuli, using both behavioural and functional neuroimaging measures. In separate conditions, symbolic cues predicted (80% validity) either the probable spatial location or semantic category of upcoming letter strings. Both spatial and semantic cues facilitated lexical decision. Orienting attention to spatial locations and semantic categories both involved a parietal-frontal network of brain areas. In addition, orienting attention to semantic categories engaged left-hemisphere frontal and temporal areas that have been linked to semantic processing. • BEHAVIOURAL TASK • Eight subjects performed a cued lexical-decision task. • Cues predicted either the spatial location (left of right visual field) or the semantic category (animal or manipulable object) of the target. Cues had 80% validity. Cues were upright or tilted crosses (+, x) presented in red or green. The colour indicated the domain of information provided (spatial, semantic) and the shape indicated the specific prediction (left/right, animal/object). Assignment of cue colour and shape to the domains and predictions was fully counterbalanced across subjects. In addition, some trials contained neutral cues, which provided no information about either location or semantic category. • Target strings appeared briefly in either the left or right visual field, were balanced by a string of X’s of equal length in the opposite field. Subjects responded by pressing a button with the right hand if the letter string constituted a real word only. 2 2, 4 5 1 4 1 Fixation (2 – 16s) 3 3 5 6 2 + time Cue (2 – 16s) xxx dog Target (100ms) BEHAVIOURAL RESULTS Subjects were faster to detect valid targets than invalid or neutral targets [F(2, 14)=7.38, p=0.01]. Post-hoc comparisons confirmed that validity effects were significant for both spatial orienting and semantic orienting. The results demonstrate that it is possible to orient attention selectively to semantic categories as well as spatial locations in order to improve word recognition. Spatial orienting cues Semantic orienting cues 1000 1000 816 900 900 763 733 727 800 672 694 800 Average RTs (ms) Average RTs (ms) 700 700 600 600 500 500 Valid Neutral Invalid Valid Invalid Neutral Orienting Attention to Semantic CategoriesT Cristescu, JT Devlin, AC Nobre Dept. Experimental Psychology and FMRIB Centre, University of Oxford, Oxford, U.K. fMRI RESULTS Common activations for orienting attention to semantic categories or spatial locations Orienting attention to semantic categories: Semantic > spatial cues Brain areaPeak coordinateZ-score 1. L frontal eye field (FEF) -21 -6 57 3.95 2. Medial premotor (SMA) -6 6 54 4.31 3. L intraparietal sulcus -30 -54 48 3.54 4. Anterior cingulate 9 15 42 3.35 5. L occipital cortex -27 -93 -9 3.43 6. R occipital cortex 36 -90 -6 4.26 Brain areaPeak coordinateZ-score 1. L inferior frontal gyrus -45 21 -3 3.22 2. L anterior medial temporal -36 6 -30 3.22 3. L posterior insula -36 -21 -3 3.31 4. L thalamus -18 -21 -6 3.60 5. Medial premotor (SMA) -3 9 57 3.37 L postcentral gyrus -63 -15 33 3.44 R postcentral gyrus 48 -27 54 4.13 • T2* weighted EPI images were acquired using a 3T Siemens Varian whole body scanner (TR=3s, TE=30s, 24 axial slices, 5mm thick, 4x4x5 resolution, 256x192 FOV). • The neural responses evoked by the cue onset were modelled as events, with a canonical HRF and its temporal derivative using SPM99 (Wellcome Dept. of Imaging Neuroscience). • fMRI RESULTS • Both types of cues activated a common network of frontal, parietal and visual areas including medial premotor and left FEF, right anterior cingulate, and left intraparietal sulcus. • The network is similar to that previously reported for visual spatial orienting attention orienting, but shows a left-hemisphere bias. • Orienting attention to semantic categories relative to spatial locations activated left hemisphere areas commonly implicated in semantic processing, such as left inferior frontal gyrus and left anterior medial temporal cortex. • No regions showed significantly greater activity for spatial than semantic cues. • CONCLUSIONS • The study demonstrates that it is possible to orient attention to semantic categories. The behavioural effects were similar to those of visual spatial orienting. Correct anticipation of the semantic category of a word target enhanced behavioural performance, significantly decreasing RTs to targets preceded by valid cues. Reaction times were slowed by invalid cues. • At the neural level, semantic orienting activated the parietal-frontal network typically associated with visual spatial orienting, albeit with a left hemisphere bias. In addition, expectancies about semantic categories engaged a network of language-related left-hemisphere brain areas involved in semantic analysis. • The results suggest that orienting attention to different stimulus attributes engages brain areas with specialisations relevant to the expectancies that can be generated. In addition, the parietal-frontal network for orienting spatial attention may provide a general support network for deploying resources selectively to optimise behaviour.