Brain stimulation made people see sexualized women less like objects in a lab test

Applying gentle electrical stimulation to the forehead appears to alter how people visually process images of sexualized women, shifting recognition patterns away from those typically associated with viewing inanimate objects. In a new double-blind experiment published in Social Neuroscience, participants who received non-invasive brain stimulation recognized upright photographs of women in underwear more accurately than participants who received a placebo stimulation. The findings provide initial evidence that the visual biases linked to sexual objectification are flexible and can be shifted by brain stimulation.

Sexual objectification occurs when a person, most commonly a woman, is viewed and evaluated primarily as a physical body or a collection of sexual parts rather than as a complete human being with thoughts, feelings, and personal agency. Beyond shaping social attitudes and media portrayals, objectification has been linked to basic differences in how the human visual system processes faces and bodies.

Normally, when people look at another person, they rely on configural processing, which means perceiving the spatial layout and proportions among facial and bodily features as an integrated whole. When looking at everyday inanimate objects like shoes or chairs, people rely more heavily on featural processing, which involves inspecting isolated parts one by one.

“It’s everywhere in advertising, film, and social media, and it’s linked to real harms, from greater tolerance of sexual violence to poorer body image and mental health in women,” said lead author Ciro Civile, an associate professor, deputy head of the psychology department, and director of research and impact for psychology in the Faculty of Health and Life Sciences at the University of Exeter. “We know a lot about those consequences, but much less about the mental machinery behind objectification.”

Cognitive scientists often measure this difference between person perception and object perception using the inversion paradigm, a test in which photographs are presented both right-side up and upside down. Because configural processing depends on seeing a face or body in its normal upright orientation, flipping a photograph of a person upside down makes it much harder to recognize, a drop in accuracy known as the inversion effect.

Flipping an inanimate object upside down causes far less difficulty because its individual features can still be identified regardless of orientation. Extending this concept to social perception, a 2012 experiment found that observers showed a reliable inversion effect for photographs of sexualized men, but no reliable inversion effect for photographs of sexualized women, suggesting that the women were being visually processed in a piecemeal, object-like way.

That interpretation sparked debate among psychologists, with some researchers arguing that differences in body symmetry or pose between the male and female photographs could account for the results, and some attempts using better-matched images failed to replicate the effect. Even so, a 2022 meta-analysis of more than 40 studies concluded that sexualized female bodies consistently elicit a smaller inversion effect than male bodies across a range of experimental setups.

Related work has explored what triggers or softens this visual pattern: an earlier experiment examining brain responses to body images indicated that sexually suggestive postures, rather than bare skin or revealing clothing alone, diminished whole-body configural processing. Other studies showed that providing personal background information about women or lowering observers’ feelings of social power helped restore normal upright recognition.

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“Earlier work, including my own on power, showed it shifts with social context,” Civile told PsyPost. “What nobody had tested was whether it could be changed by acting directly on perception.”

Alongside social cues, researchers have investigated whether visual recognition biases can be altered directly through transcranial direct current stimulation, a non-invasive technique that delivers a weak electrical current through sponge pads placed on the scalp to temporarily change how easily brain cells fire. For ordinary faces, applying this stimulation over the left forehead tends to impair recognition of upright faces and shrink the inversion effect, but an earlier series of experiments led by Civile found the opposite pattern when faces were distorted using the Thatcher illusion, in which the eyes and mouth are flipped upside down.

In the researchers’ account, those inverted eyes and mouths stand out as unusual shared features across all the altered faces, disrupting normal whole-face perception when viewed upright. Applying electrical stimulation restored upright recognition of those distorted faces and brought the inversion effect back to typical levels.

Civile and Arwen Stephens of the University of Exeter reasoned that sexualized portrayals of women might disrupt normal person perception in a similar manner, by drawing observers’ attention to prominent, shared sexualized features at the expense of the distinctive spatial cues that identify an individual. If sexualization impairs upright recognition by promoting piecemeal, feature-based viewing, then the same forehead stimulation that restored recognition for distorted faces should also boost upright recognition and enlarge the inversion effect for sexualized women.

To test this hypothesis, Civile and Stephens recruited 76 right-handed university students at the University of Exeter, including 54 women and 22 men with an average age of about 22 years. An advance statistical power calculation indicated that at least 68 participants were needed for a 90 percent chance of detecting a small-to-medium difference between groups, and the final sample of 76 provided a 93 percent chance. Although the statistical analyses were not preregistered, the researchers followed the analysis plan established in their previous brain stimulation studies and made their anonymized participant data and analysis scripts publicly available online.

Participants were randomly assigned in equal numbers to either an active brain stimulation group or a placebo stimulation group using a double-blind computer system, meaning neither the participants nor the researchers running the sessions knew which condition a person was assigned to. Each participant had two saline-soaked sponge electrodes strapped to their head, with the positive electrode positioned on the left side of the forehead above the left eyebrow and the return electrode placed just above the right eyebrow.

This placement was originally selected in cognitive research to target the left dorsolateral prefrontal cortex, a brain region involved in learning visual patterns and categories. Because the electrical current from sponge pads spreads widely, however, the researchers describe the procedure by where the pads sit on the head rather than assuming it hits a single brain area.

Civile wanted to address the technique directly, “because ‘brain stimulation’ can sound alarming.” “Transcranial direct current stimulation (tDCS) is non-invasive: nothing enters the body,” he said. “Most people feel at most a mild tingle. It has nothing to do with electric shocks, and it isn’t electroconvulsive therapy, which uses far stronger currents under general anesthesia.”

“tDCS doesn’t make brain cells fire; it only slightly changes how readily they respond,” he added. “Our participants were screened beforehand, and none reported any adverse effects.”

In the active group, a gentle 1.5-milliampere current ramped up over 5 seconds, ran continuously for 10 minutes, and ramped down over 5 seconds. In the placebo group, the current ramped up and down in the same way but lasted for only 30 seconds at the very start, mimicking the initial tingling sensation on the skin without delivering meaningful stimulation during the task.

As soon as the stimulation began, participants started a two-part recognition test featuring 64 standardized color photographs of white male and female models wearing black underwear against a white background and standing in open postures looking at the camera. Participants first watched 32 upright and upside-down photographs appear one by one during a four-minute study phase, and then completed an eight-minute test phase where those 32 images were mixed with 32 new ones and participants had up to 3 seconds per image to press a key indicating whether they had seen the model earlier.

The researchers evaluated performance by calculating each participant’s recognition sensitivity, a standard memory measure that weighs how often a person accurately recognized a previously seen photo against how often they mistakenly claimed a new photo was familiar. Across the experiment as a whole, the difference in overall memory accuracy between the active stimulation group and the placebo group was not statistically significant, suggesting that the electrical current did not simply make people better or worse at remembering images in general.

In the placebo group, however, the classic pattern associated with sexual objectification emerged: the inversion effect, measured as the drop in sensitivity from upright to upside-down photos, was more than twice as large for male models (0.69) as it was for female models (0.27). The study’s main test showed that this male-female gap differed between the two groups to a statistically significant degree, though the effect was modest and its estimated size came with a wide margin of uncertainty.

Among participants who received the 10-minute active brain stimulation, the gap between male and female models was no longer statistically significant. In the active group, the inversion effect for sexualized female models was 0.87, more than three times that in the placebo group, while the inversion effect for male models was similar (0.75 versus 0.69 under placebo). A follow-up Bayesian statistical test indicated that the data in the active group were roughly six times more consistent with the absence of an objectification bias than with the bias typically seen in prior work, though the authors note that this does not establish that the female and male inversion effects were identical.

Closer inspection of the scores showed that the larger inversion effect for women in the active stimulation group was accompanied specifically by sharper recognition of upright female models. Participants who received active stimulation correctly identified 74 percent of previously seen upright female photos, compared to 67 percent in the placebo group, while also making fewer false alarms. Recognition accuracy for upside-down female photos, by contrast, did not differ in a statistically significant way between the active and placebo groups, and the inversion effect for male models did not differ between groups in a statistically significant way.

“The way we see sexualized images of women isn’t hard-wired,” Civile said. “In our study, ten minutes of a weak current to the forehead made people better at recognizing sexualized women in right-way-up photos. They then recognized the women the way they recognized the men, which is the way we normally recognize people rather than objects.”

“Earlier studies showed the same pattern shifts when people feel powerful or powerless, or are given humanizing information about the women,” he continued. “Together, these findings suggest objectification is partly a learned habit of perception, and habits can change. It’s also worth knowing this isn’t only something men do. In earlier studies, women showed the same pattern toward sexualized women.”

To explain why brain stimulation was associated with better recognition of upright sexualized women when the very same procedure usually impairs recognition of ordinary upright faces, the authors point to a theoretical framework of perceptual learning. According to the researchers, years of everyday experience with normal upright faces train the brain to tune out features that all faces have in common and focus instead on subtle, distinctive traits that set one individual apart from another. When people view sexualized women, the authors suggest, their attention may be captured by prominent features shared across the images, such as exposed body parts or stereotypical cues of sexual attractiveness, causing different women to blur together in memory and lowering upright recognition accuracy.

In the authors’ reading, applying weak electrical stimulation over the forehead dampens this tendency to over-weigh prominent shared features, allowing observers to take in the distinctive spatial configuration of each woman’s face and body and recognize upright individuals more accurately. The researchers caution, however, that their experiment measured only recognition accuracy and did not directly measure attention to specific body parts or configural processing. As a result, their perceptual-learning explanation remains a working hypothesis, and the higher recognition accuracy could also reflect differences in visual attention, memory encoding, or decision-making during the test.

In previous studies, Civile and his colleagues had tested the same forehead stimulation on the tendency for people to recognize faces of their own race or age group more easily than faces from other groups. “We predicted the result, but the direction is still striking,” Civile said. “In our earlier studies, the same stimulation made people worse at recognizing faces of their own race or age group the right way up, removing the edge that experience gives us. Here it made people better at recognizing sexualized women.”

“The same current pushing performance in opposite directions tells us it isn’t simply boosting or impairing recognition,” he explained. “It seems to dampen whatever perceptual habits experience has built, helpful or not. The effect was also specific: the pattern for men didn’t change.”

There are a few things to keep in mind when interpreting these findings. First, the experiment tested only photographs of models in underwear rather than comparing them against fully clothed men and women, and the male and female photos could differ in body contours, pose, or visual complexity. Because of this, the gap between men and women in the placebo group cannot be attributed specifically to sexualization, though image differences alone cannot explain why the active stimulation group outperformed the placebo group on upright female photos. In addition, the inversion effect is an indirect visual marker rather than a direct measure of whether people hold objectifying attitudes or treat women differently in everyday life.

“This is not a cure for sexism, and it isn’t a way to change what people think,” Civile emphasized. “We measured how people recognized photos in a lab, not their attitudes or how they treat women.”

“The practical significance is about understanding, not treatment,” he added. He noted that the team “didn’t track how long the change lasts, but the effects of a single session of this kind of stimulation are thought to last up to a couple of hours. What matters is the proof of principle: a perceptual bias tied to objectification can be shifted by acting directly on perception.”

The way the brain stimulation was delivered also leaves a few practical questions open. Because the electrical current from standard sponge pads spreads widely across the skull and varies with individual head anatomy, the experiment cannot pinpoint which specific brain structure was involved, or whether the stimulation acted while participants were first viewing the images or while they were recalling them minutes later.

In addition, active stimulation lasted 10 minutes while the placebo current lasted only 30 seconds, and the researchers did not formally survey participants afterward to check whether they guessed their group assignment. Although an earlier study by Civile using the same setup found that participants’ ratings of how the stimulation felt did not differ between active and placebo groups, the authors note that future experiments should measure participants’ sensations and expectations directly.

The sample also excluded people with psychiatric or neurological conditions or those taking medication, so the results may not extend to those groups. And because it included 54 women and 22 men without separate analyses by participant gender, future research could recruit equal numbers of men and women to check whether observer gender plays a role. Future studies could also compare clothed and sexualized images alongside direct measures of social attitudes, manipulate the spatial layout of body images directly, and use computer models of electrical current flow in the brain to identify the neural pathways involved.

“Another step is to alter the body images directly, in a Thatcher-style manipulation, to test whether disrupted whole-body processing explains the effect,” Civile said. “Longer term, I want to understand how experience and social context, such as power, shape the way we perceive other groups. That covers gender, race, and age, and ultimately how such biases might be countered.”

The study, “Disrupting objectification: transcranial Direct Current Stimulation (tDCS) enhances the inversion effect toward sexualized women,” was authored by Ciro Civile and Arwen Stephens.