The effects of transcranial direct current stimulation on perceptual learning for upright faces and its role in the composite face effect.

Abstract

In the 3 experiments reported here we show that a specific neurostimulation method, whose influence can be understood in terms of a well-known theory of stimulus representation, is able to affect face recognition skills by impairing participants’ performance for upright faces. We used the transcranial Direct Current Stimulation (tDCS) procedure we have recently developed that allows perceptual learning, as indexed by the face inversion effect, to be modulated. We extended this tDCS procedure to another phenomenon, the composite face effect, which constitutes better recognition of the top half of an upright face when conjoined with a congruent (in terms of the response required) rather than incongruent bottom half. All three experiments used the Face-Matching task traditionally used to study this phenomenon. Experiment 1a (n = 48) showed that anodal tDCS (using a double-blind between-subjects design) delivered at Fp3 (10 mins at 1.5 mA) affected overall performance for upright faces compared with sham but had no effect on the composite face effect itself. Experiment 1b (n = 48) replicated our usual tDCS-induced effects on the face inversion effect but this time using a Face-Matching task instead of the old/new recognition task previously used to obtain the effect. Experiment 2 (n = 72) replicated the findings from Experiment 1a, and, using an active control group, showed that the Fp3 anodal tDCS effects on performance to upright faces are not obtained when a different brain area is targeted. We interpret our results in the light of previous literature on the tDCS effects on perceptual learning and face recognition and suggest that different mechanisms are involved in the face inversion effect and the composite face effect.

Using transcranial direct current stimulation (tDCS) to influence decision criterion in a target detection paradigm.

“…In this case as well, the reduction was mainly due to an impaired recognition performance for upright faces in the anodal versus sham group (Civile, McLaren, & McLaren, 2018, Experiments 1 and 2). This result has been replicated across multiple studies and it is now an established finding (Civile, McLaren, & McLaren, 2018; Civile et al, 2019; Civile, McLaren, et al, 2020; Civile, Waguri, et al, 2020; Civile, Quaglia, et al, 2021; Civile, McLaren, et al, 2021). Furthermore, Civile, McLaren, and McLaren (2018) Experiment 3 (the active control study) tested whether targeting a different brain area would result in the same effects obtained in Experiment 1 and 2.…”

“…Finally, previous work using the same tDCS procedure applied to the inversion effect, has consistently demonstrated how the effects of anodal tDCS are found only on the size of the inversion effect and specifically in modulating performance to familiar upright stimuli (e.g., faces or checkerboards). However, no effects of anodal tDCS have ever been found on overall performance nor on inverted stimuli (Civile, Verbruggen, et al, 2016; Civile, McLaren, et al, 2018; Civile et al, 2019; Civile, Cooke, et al, 2020; Civile, McLaren, et al, 2020; Civile, Waguri, et al, 2020; Civile, Quaglia, et al, 2021; Civile, McLaren, et al, 2021). Even if we allowed a potential explanation based on the sensation experienced in the anodal tDCS group versus sham, it hard to see why that would only systematically affect the inversion effect specifically via performance for upright stimuli.…”

“…In the last 6 years research has shown that 1.5 mA anodal tDCS to Fp3 reduces both the inversion effect typically obtained with faces in recognition experiments and eliminates the inversion effect owing to perceptual learning in checkerboards (Civile, Cooke, et al, 2020; Civile, McLaren, et al, 2018; Civile, McLaren, et al, 2020; Civile, McLaren, et al, 2021; Civile et al, 2019; Civile, Quaglia, et al, 2021; Civile, Verbruggen, et al, 2016; Civile, Waguri, et al, 2020). Importantly, these studies provided evidence of this specific tDCS procedure modulating the discriminability index, d ′ in recognition tasks using either checkerboard or face stimuli, advancing our understanding of the role that perceptual learning plays in face recognition.…”

“…Both experiments adopted the same tDCS procedure previously used to modulate perceptual learning and face recognition skills (Civile, Cooke, et al, 2020; Civile, McLaren, et al, 2018; Civile, McLaren, et al, 2020; Civile, McLaren, et al, 2021; Civile et al, 2019; Civile, Quaglia, et al, 2021; Civile, Verbruggen, et al, 2016; Civile, Waguri, et al, 2020). The stimulation is delivered by a battery-driven constant current stimulator (neuroConn DC- Stimulator Plus) using a pair of surface sponge electrodes (35 cm 2 ) soaked in saline water and applied to the scalp at the target areas for stimulation.…”

Special issue on recent advances in perceptual learning.

“…It is important to note that this effect of latent inhibition is not found in older children (7-10 years old) or in adults. Civile et al (2021) provide further evidence in support of a particular tDCS procedure's being able to modulate perceptual learning in an experimental paradigm often adopted to test individuals with face-blindness. The authors establish for the first time that the tDCS-induced effects in modulating perceptual learning are effective with a procedure entirely based on upright faces.…”