Cite this article as: Matt Craddock, Ellen Poliakoff, Wael El-deredy, Ekaterini Klepousniotou and Donna M. Lloyd, Pre-stimulus alpha oscillations over somatosensory cortex predict tactile misperceptions, Neuropsychologia, http://dx.doi.org/10. 1016/j.neuropsychologia.2016.12.030 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractFluctuations of pre-stimulus oscillatory activity in the somatosensory alpha band (8-14 Hz) observed using human EEG and MEG have been shown to influence the detection of supraand peri-threshold somatosensory stimuli. However, some reports of touch occur even without a stimulus. We investigated the possibility that pre-stimulus alpha oscillations might also influence these false reports of touch -known as tactile misperceptions. We recorded EEG while participants performed the Somatic Signal Detection Task (SSDT), in which participants must detect brief, peri-threshold somatosensory targets. We found that prestimulus oscillatory power in the somatosensory alpha range exhibited a negative linear 2 relationship with reporting of touch at electrode clusters over both contralateral and ipsilateral somatosensory regions. As pre-stimulus alpha power increased, the probability of reporting a touch declined; as it decreased, the probability of reporting a touch increased. This relationship was stronger on trials without a somatosensory stimulus than on trials with a somatosensory stimulus, although was present for both trial types. Spatio-temporal clusterbased permutation analysis also found that pre-stimulus alpha was lower on trials when touch was reported -irrespective of whether it was present -over contralateral and ipsilateral somatosensory cortices, as well as left frontocentral areas. We argue that alpha power may reflect changes in response criterion rather than sensitivity alone. Low alpha power relates to a low barrier to reporting a touch even when one is not present, while high alpha power is linked to less frequent reporting of touch overall.

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Two experiments examined the effects of size changes on haptic object recognition. In Experiment 1, participants named one of three exemplars (a standard-size-and-shape, different-size, or different-shape exemplar) of 36 categories of real, familiar objects. They then performed an old/new recognition task on the basis of object identity for the standard exemplars of all 36 objects. Half of the participants performed both blocks visually; the other half performed both blocks haptically. The participants were able to efficiently name unusually sized objects haptically, consistent with previous findings of good recognition of small-scale models of stimuli (Lawson, in press). However, performance was impaired for both visual and haptic old/new recognition when objects changed size or shape between blocks. In Experiment 2, participants performed a short-term haptic shapematching task using 3-D plastic models of familiar objects, and as in Experiment 1, a cost emerged for ignoring the irrelevant size change. Like its visual counterpart, haptic object recognition incurs a significant but modest cost for generalizing across size changes.

Emotionally arousing stimuli are known to rapidly draw the brain's processing resources, even when they are task-irrelevant. The steady-state visual evoked potential (SSVEP) response, a neural response to a flickering stimulus which effectively allows measurement of the processing resources devoted to that stimulus, has been used to examine this process of attentional shifting. Previous studies have used a task in which participants detected periods of coherent motion in flickering random dot kinematograms (RDKs) which generate an SSVEP, and found that task-irrelevant emotional stimuli rapidly withdraw attentional resources from the task-relevant RDKs. However, it is not clear whether the changes in the SSVEP response are conditional on higher-level extraction of emotional cues as indexed by well-known event-related potential (ERPs) components, or if affective bias in competition for visual attention resources could be a consequence of an inherent, relatively time-invariant shifting process. In the present study, we used two different types of emotional distractors -IAPS pictures and facial expressions -for which emotional cue extraction occurs at different speeds, being typically earlier for faces (at ~170 ms, as indexed by the N170) than for IAPS images (220-230 ms, Early Posterior Negativity, EPN). We found that attentional resources were withdrawn from the foreground task towards task-irrelevant emotional background images from the International Affective Picture System (IAPS) following the extraction of emotional cues as indexed by visual ERP components. We also found that emotional modulation of attentional resources as measured by the SSVEP occurred earlier for faces (around 180 ms) than for IAPS pictures (around 400 ms). This is consistent with lowlevel attentional resources being re-allocated after emotional cue extraction rather than being linked to a time-fixed shifting process.

Visual object processing may follow a coarse-to-fine sequence imposed by fast processing of low spatial frequencies (LSF) and slow processing of high spatial frequencies (HSF). Objects can be categorized at varying levels of specificity: the superordinate (e.g. animal), the basic (e.g. dog), or the subordinate (e.g. Border Collie). We tested whether superordinate and more specific categorization depend on different spatial frequency ranges, and whether any such dependencies might be revealed by or influence signals recorded using EEG. We used event-related potentials (ERPs) and time-frequency (TF) analysis to examine the time course of object processing while participants performed either a grammatical gender-classification task (which generally forces basic-level categorization) or a living/non-living judgement (superordinate categorization) on everyday, real-life objects. Objects were filtered to contain only HSF or LSF. We found a greater positivity and greater negativity for HSF than for LSF pictures in the P1 and N1 respectively, but no effects of task on either component. A later, fronto-central negativity (N350) was more negative in the gender-classification task than the superordinate categorization task, which may indicate that this component relates to semantic or syntactic processing. We found no significant effects of task or spatial frequency on evoked or total gamma band responses. Our results demonstrate early differences in processing of HSF and LSF content that were not modulated by categorization task, with later responses reflecting such higher-level cognitive factors.