Representational structure or task structure? Bias in neural representational similarity analysis and a Bayesian method for reducing bias
Fig 4
Limited performance of BRSA at very low SNR and small amount of data.
(A) The average correlation between the off-diagonal elements of the estimated and the true similarity matrices (mean ± std) as the number of simulated subjects increases. Each simulated subject had one run of data. Legend shows average SNR in task-responsive voxels. Half of the voxels do not include any signal related to the design matrix. The correlation reaches asymptotic levels slightly below 1 with increasing numbers of participants except when the SNR is extremely low (0.07), indicating that the bias is not fully eliminated. (B) The average correlation between the estimated similarity matrix and the expected bias structure assuming white noise. The estimated similarity structure is most dominated by the bias structure at the lowest SNR simulated (0.07). The negative correlation at the highest SNR reflects the weak negative correlation between the true similarity structure and expected bias structure (-0.055).