A critical band of phase alignment for discrimination but not recognition of human faces

We investigated the processes underlying the discrimination and recognition of human faces as a function of spatial phase alignment to assess whether face processing can be understood in terms of the amplitude spectrum alone. Specifically, we varied the amount of aligned Fourier phase in different regions of the face frequency spectrum and argue that the properties of the underlying neural processes are best understood in terms of the number of phase alignments as opposed to octave bandwidths. Additionally, we observed performance differences for face discrimination tasks compared to face recognition tasks. For face recognition, our results show that a narrower range of phase alignment is needed for face frequencies near 9 cpf when compared to 3 and 27 cpf, thereby supporting the notion of a critical frequency for face recognition. However, for face discrimination where participants were required to discriminate between an average face and different unique faces along a face morph continuum, performance depended on a fixed signal-to-noise ratio of phase alignment within a contiguous range of face frequencies (termed critical band of phase alignments), regardless of the central face frequency of that range within the face frequency spectrum when compared to non-phase randomized control thresholds.