Figure 2 Experimental and methodological framework. A, Study rationale. We studied reference frames for planning grasping movements to targets provided in two modalities: visual (top) or somaesthetic (bottom). Within each modality, reference frames were tested by aggregating evidence across four pairs of trials, either equal or distinct in gaze-centered or body-centered coordinates [right panels, black rectangles indicate pairs of trials (not shown to subject)]. Two pairs, outer sides and center sides, were not used in the reference frame analysis, but were used to independently define regions of interest and test for gaze-direction effects. B, The two-sided evidence combination method. We specified which pairs of trials (indicated by column headers) should be distinct (≠) or common (=) in GC and BC reference frames (1). Next, we calculated the classification score (a) for each distinct pair and the cross-classification score (o) for each common pair (2), and combined the values to obtain an evidence score per reference frame (3). C, Example classification and cross-classification procedure, within (top) and across (bottom) modalities. For each pair of trials (e.g., left w.r.t. body), a classifier was trained and cross-validated (top, first column). The resulting accuracy value represents the classification result (≠ or a) for the specific pair. Next, the trained classifier was tested on the four possible pairs with one of the two trial configurations replaced (e.g., gaze center-target left replaced by gaze right-target right, second column). In the example, if cross-classification is high (=), it gives evidence for gaze-centered coding, as the pair describing the replacement is equal in gaze-centered coordinates (third column). The procedure was also applied across modalities (bottom), training on one modality (first column) and testing on the other (second column) and vice versa, to test for common representations across modalities (third column). D, Schematic overview of the analysis pipeline, highlighting the most important steps in the analysis.