A critique of functional localisers

The Wellcome Department of Imaging Neuroscience, Institute of Neurology, UCL, 12 Queen Square, London WC1N 3BG, UK.
NeuroImage (Impact Factor: 6.36). 06/2006; 30(4):1077-87. DOI: 10.1016/j.neuroimage.2005.08.012
Source: PubMed


In this critique, we review the usefulness of functional localising scans in functional MRI studies. We consider their conceptual motivations and the implications for experimental design and inference. Functional localisers can often be viewed as acquiring data from cells that have been removed from an implicit factorial design. This perspective reveals their potentially restrictive nature. We deconstruct two examples from the recent literature to highlight the key issues. We conclude that localiser scans can be unnecessary and, in some instances, lead to a biased and inappropriately constrained characterisation of functional anatomy.

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Available from: Pia Rotshtein, Oct 05, 2015
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    • "there was one interaction effect whose test was motivated by the behavioural results, namely a hand-by-view interaction. to provide a realistic protection against false positives in these higher-level interaction effect (given the presence of a baseline at the first level, the view-by-hand interactions are second-level interactions), we used a smallvolume correction constrained by the functional localizer of the main effect of the palm-minus-back view (see Friston et al. 2006): the small-volume correction for this interaction effect was calculated using a 10-mm-radius sphere centred on two local maxima identified by the functional localizer. "
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    ABSTRACT: There is a common saying for expressing familiarity with something. It refers to our hands, and strangely enough, in English, one says to know something like the back of the hand, whereas in other cultures, for example, Italy, Spain and France, the same expression is with the palm. Previous behavioural data have suggested that our ability to visually discriminate a right from a left hand is influenced by perspective. This behavioural finding has remained without neurophysiological counterparts. We used an implicit motor imagery task in which 30 right-handed subjects were asked to decide whether a picture portrayed a right rather than a left hand during an fMRI event-related experiment. Both views (back and palm) were used, and the hands were rotated by 45° in 8 possible angles. We replicated previous behavioural evidence by showing faster reaction times for the back-view and view-specific interaction effects with the angle of rotation: for the back view, the longest RTs were with the hand facing down at 180°; for the palm view, the longest RTs were at 90° with the hand pointing away from the midline. In addition, the RTs were particularly faster for back views of the right hand. fMRI measurements revealed a stronger BOLD signal increase in left premotor and parietal cortices for stimuli viewed from the palm, whereas back-view stimuli were associated with stronger occipital activations, suggesting a view-specific cognitive strategy: more visually oriented for the back of the hand; more in need of the support of a motoric imagery process for the palms. Right-hand back views were associated with comparatively smaller BOLD responses, attesting, together with the faster reaction times, to the lesser need for neural labour because of greater familiarity with that view of the hand. These differences suggest the existence of brain-encoded, view-dependent representations of body segments.
    Experimental Brain Research 08/2014; 232(12). DOI:10.1007/s00221-014-4065-z · 2.04 Impact Factor
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    • "As the above localization analyses were based on BOLD signal averaged across all block-related conditions (attention left vs. right, and grouped vs. ungrouped) this method of localization could not bias the outcome of our tests for hypothesized differences between conditions, either block-related or event-related. This method of defining a region of interest, based on a contrast that is orthogonal to those used to test an experimental hypothesis , is an established approach in the literature (Friston et al., 2006). We used our own circularly translating stimuli, rather than a traditional independent motion localizer based on moving random-dot kinematograms, as this could isolate regions sensitive to the specific type of motion used in our main experiment , providing a principled and statistically independent way to identifying relevant voxels that might be subject to our particular modulations of spatial attention and stimulus grouping. "
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    ABSTRACT: Theories of object-based attention often make two assumptions: that attentional resources are facilitatory, and that they spread automatically within grouped objects. Consistent with this, ignored visual stimuli can be easier to process, or more distracting, when perceptually grouped with an attended target stimulus. But in past studies, the ignored stimuli often shared potentially relevant features or locations with the target. In this fMRI study, we measured the effects of attention and grouping on Blood Oxygenation Level Dependent (BOLD) responses in the human brain to entirely task-irrelevant events. Two checkerboards were displayed each in opposite hemifields, while participants responded to check-size changes in one pre-cued hemifield, which varied between blocks. Grouping (or segmentation) between hemifields was manipulated between blocks, using common (vs. distinct) motion cues. Task-irrelevant transient events were introduced by randomly changing the color of either checkerboard, attended or ignored, at unpredictable intervals. The above assumptions predict heightened BOLD signals for irrelevant events in attended vs. ignored hemifields for ungrouped contexts, but less such attentional modulation under grouping, due to automatic spreading of facilitation across hemifields. We found the opposite pattern, in primary visual cortex. For ungrouped stimuli, BOLD signals associated with task-irrelevant changes were lower, not higher, in the attended vs. ignored hemifield; furthermore, attentional modulation was not reduced but actually inverted under grouping, with higher signals for events in the attended vs. ignored hemifield. These results challenge two popular assumptions underlying object-based attention. We consider a broader biased-competition framework: task-irrelevant stimuli are suppressed according to how strongly they compete with task-relevant stimuli, with intensified competition when the irrelevant features or locations comprise the same object.
    Frontiers in Integrative Neuroscience 02/2014; 8:12. DOI:10.3389/fnint.2014.00012
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    • "It was implemented by generating sample-evoked functional regions of interest (ROIs), then analyzing the level of activity within these functional ROIs during different epochs from the same task. (For a discussion of such a “factorial design” approach, in which one epoch of the experimental task is used to define an ROI (rather than, e.g., a separate functional localizer scan), and then this ROI is interrogated with orthogonal contrasts, see [29]). The analyses proceeded in six steps, the first five performed on an individual subject basis. "
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    ABSTRACT: The positional-specificity effect refers to enhanced performance in visual short-term memory (VSTM) when the recognition probe is presented at the same location as had been the sample, even though location is irrelevant to the match/nonmatch decision. We investigated the mechanisms underlying this effect with behavioral and fMRI studies of object change-detection performance. To test whether the positional-specificity effect is a direct consequence of active storage in VSTM, we varied memory load, reasoning that it should be observed for all objects presented in a sub-span array of items. The results, however, indicated that although robust with a memory load of 1, the positional-specificity effect was restricted to the second of two sequentially presented sample stimuli in a load-of-2 experiment. An additional behavioral experiment showed that this disruption wasn't due to the increased load per se, because actively processing a second object - in the absence of a storage requirement - also eliminated the effect. These behavioral findings suggest that, during tests of object memory, position-related information is not actively stored in VSTM, but may be retained in a passive tag that marks the most recent site of selection. The fMRI data were consistent with this interpretation, failing to find location-specific bias in sustained delay-period activity, but revealing an enhanced response to recognition probes that matched the location of that trial's sample stimulus.
    PLoS ONE 12/2013; 8(12):e83483. DOI:10.1371/journal.pone.0083483 · 3.23 Impact Factor
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