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. 2017 Apr 20;8:15027. doi: 10.1038/ncomms15027

Figure 3. MEG recordings.

Figure 3

(a) The behavioural paradigm was as before except that Probe tones were introduced between the Context and Test. The Probe-tone frequency was either the centre of the frequency region of the context (‘Context+') or the centre of the opposite frequency region (‘Context−'). Trials were coded as ‘Bias+' if listeners reported the expected pitch shift encompassing the frequency region of the context, or ‘Bias−' if listeners reported the opposite pitch shift. (b) Time course of the MEG response. The MEG sensor signals were filtered between 2 and 120 Hz, squared and then averaged for the 50 auditory channels for each participant. Here and in all panels the shaded area or error bars indicate 95% confidence intervals of the mean across participants. (c) Probe-tone response. A fast Fourier transform was performed on the concatenated MEG responses during the probe sequence over all trials, for each participant. For display purposes, the result was normalized for each participant by baseline activity over 3–5 Hz, excluding the frequency bin at 4 Hz. (d) The topography of the 4 Hz response during the probe sequence. The complex responses from the FFT analysis are plotted for each sensor, with the arrows representing the magnitude and phase value of the 4-Hz component. Contours are projections on lines of constant phase (see Supplementary Methods). (e) Behavioural results during the MEG recordings. The bias caused by context tones is of the same magnitude as for previous experiments, whereas the bias caused by the Probe sequence is weak, with confidence intervals for P(Bias) overlapping with 0.5. (f) MEG correlate of the behavioural bias. A PRR was defined as the 4-Hz probe response for Context+ trials, divided by the 4-Hz probe for Context− trials. A PRR value lower than one is observed for Bias+ trials, indicating a reduced responsivity in the frequency region of the context when the context was effective in producing a behavioural bias. The reverse pattern is observed, for identical stimuli, when the behavioural bias is in the opposite direction.