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. 2024 Jan 30;14(2):146.
doi: 10.3390/brainsci14020146.

Extensive Visual Training in Adulthood Reduces an Implicit Neural Marker of the Face Inversion Effect

Simen Hagen  1 , Renaud Laguesse  2 , Bruno Rossion  1   3   4
Affiliations

Extensive Visual Training in Adulthood Reduces an Implicit Neural Marker of the Face Inversion Effect

Simen Hagen et al. Brain Sci. .

Abstract

Face identity recognition (FIR) in humans is supported by specialized neural processes whose function is spectacularly impaired when simply turning a face upside-down: the face inversion effect (FIE). While the FIE appears to have a slow developmental course, little is known about the plasticity of the neural processes involved in this effect-and in FIR in general-at adulthood. Here, we investigate whether extensive training (2 weeks, ~16 h) in young human adults discriminating a large set of unfamiliar inverted faces can reduce an implicit neural marker of the FIE for a set of entirely novel faces. In all, 28 adult observers were trained to individuate 30 inverted face identities presented under different depth-rotated views. Following training, we replicate previous behavioral reports of a significant reduction (56% relative accuracy rate) in the behavioral FIE as measured with a challenging four-alternative delayed-match-to-sample task for individual faces across depth-rotated views. Most importantly, using EEG together with a validated frequency tagging approach to isolate a neural index of FIR, we observe the same substantial (56%) reduction in the neural FIE at the expected occipito-temporal channels. The reduction in the neural FIE correlates with the reduction in the behavioral FIE at the individual participant level. Overall, we provide novel evidence suggesting a substantial degree of plasticity in processes that are key for face identity recognition in the adult human brain.

Keywords: EEG; face identify recognition; face inversion; frequency tagging; neural plasticity.

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Conflict of interest statement

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
(A) Schematic illustration of the test and training pipeline, where eight training sessions, with up to four different training tasks per session (see Table 1), were flanked by pre- and post-training tests. The pre- and post-training tests consisted of separate neural and behavioral measures, as illustrated in the next panels. (B) Schematic illustration of the FPVS-EEG experimental paradigm. Separate sequences showed upright and inverted faces. The test was administered before and after training. The participants fixated a cross centered between the eyes and pressed the space bar every time they detected random changes in color from blue to red. (C) The four-alternatives forced-choice (4-AFC) delayed matching task [41], which was performed for both upright and inverted faces before and after training (different sets of faces).
Figure 2
Figure 2
Group behavioral performance as a function of session (pre-, post-) and image orientation (upright, inverted) for (A) accuracy, (B) correct response times, and (C) inverse efficiency scores (RT/proportion correct). Error bars represent standard error of the means. **, ***, n.s. represent p < 0.01 p < 0.001, p > 0.05, respectively.
Figure 3
Figure 3
The EEG response averages across conditions (session, image orientation). (A) The scalp topography for the face discrimination response (left) and the general visual response (right). (B) The EEG amplitude spectrum over the average of two occipito-temporal electrodes (one in each hemisphere: P9, P10). There were clear responses at the face identity discrimination frequency (F/5 = 1.176 Hz and its harmonics) and at the general visual stimulation frequency (F = 5.88 Hz and its harmonics; only the two first harmonics are shown).
Figure 4
Figure 4
Neural face discrimination responses (F/5 and harmonics). (A) Scalp topographies displaying the group average face discrimination amplitudes as a function of session (pre-, post-) and image orientation (upright, inverted). (B) The average face discrimination amplitude averaged across peak channels as a function of session (pre-, post-) and image orientation (upright, inverted). Error bars represent standard error of the means. *, *** represent p < 0.05, p < 0.001, respectively.
Figure 5
Figure 5
Neural general visual responses (F and harmonics). (A) Scalp topographies displaying the group average general visual response amplitudes as a function of session (pre-, post-) and image orientation (upright, inverted). (B) The average general visual response amplitude averaged across peak channels as a function of session (pre-, post-) and image orientation (upright, inverted). Error bars represent standard error of the means. n.s. represents p > 0.05.
Figure 6
Figure 6
Correlation between behavioral and neural FIE change. (A) The correlation between the change in inversion effect from pre- to post-test for the behavioral accuracy measure (x-axis) and for the neural face discrimination response (F/5 and harmonics) (y-axis). (B) The correlation between the change in inversion effect from pre- to post-test for the behavioral accuracy measure (x-axis) and for the neural general visual response (F and harmonics) (y-axis). A positive change indicates a decrease in the FIE, while a negative change indicates an increase in the FIE. Each colored dot represents an individual participant. Each dot represents a participant and the gray line represents the regression line.
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