Abstract
BackgroundWhile there is a general agreement that picture-plane inversion is more detrimental to face processing than to other seemingly complex visual objects, the origin of this effect is still largely debatable. Here, we address the question of whether face inversion reflects a quantitative or a qualitative change in processing mode by investigating the pattern of event-related potential (ERP) response changes with picture plane rotation of face and house pictures. Thorough analyses of topographical (Scalp Current Density maps, SCD) and dipole source modeling were also conducted.ResultsWe find that whilst stimulus orientation affected in a similar fashion participants' response latencies to make face and house decisions, only the ERPs in the N170 latency range were modulated by picture plane rotation of faces. The pattern of N170 amplitude and latency enhancement to misrotated faces displayed a curvilinear shape with an almost linear increase for rotations from 0° to 90° and a dip at 112.5° up to 180° rotations. A similar discontinuity function was also described for SCD occipito-temporal and temporal current foci with no topographic distribution changes, suggesting that upright and misrotated faces activated similar brain sources. This was confirmed by dipole source analyses showing the involvement of bilateral sources in the fusiform and middle occipital gyri, the activity of which was differentially affected by face rotation.ConclusionOur N170 findings provide support for both the quantitative and qualitative accounts for face rotation effects. Although the qualitative explanation predicted the curvilinear shape of N170 modulations by face misrotations, topographical and source modeling findings suggest that the same brain regions, and thus the same mechanisms, are probably at work when processing upright and rotated faces. Taken collectively, our results indicate that the same processing mechanisms may be involved across the whole range of face orientations, but would operate in a non-linear fashion. Finally, the response tuning of the N170 to rotated faces extends previous reports and further demonstrates that face inversion affects perceptual analyses of faces, which is reflected within the time range of the N170 component.
Highlights
While there is a general agreement that picture-plane inversion is more detrimental to face processing than to other seemingly complex visual objects, the origin of this effect is still largely debatable
Both scalp current density (SCD) mapping and dipole source modeling were performed on scalp recorded event-related potential (ERP) data of interest
For the individual ERP data, we report the average time-intervals used for the dipole fit and the statistical mean of residual variance (+ 1 standard error of mean (SEM)) obtained for each face rotation condition
Summary
While there is a general agreement that picture-plane inversion is more detrimental to face processing than to other seemingly complex visual objects, the origin of this effect is still largely debatable. It has long been claimed that the effect of inverting faces from their canonical upright orientation constitutes a diagnostic marker for the processing differences between faces and other seemingly complex and monoriented objects [1]. In his seminal paper, Yin [2] showed that while most objects (houses, airplanes, dogs, etc.) are somewhat harder to recognize upside down than rightside up, face recognition is more drastically reduced by stimulus inversion. Upright and inverted faces are processed in a similar fashion albeit less effectively in the upsidedown orientation [1]
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