Sunday, September 12, 2021

We observed an association between frequent pornography use and not having had sex in the last year among men (which was in contrast with previous studies), but not women

Malki K, Rahm C, Öberg KG, et al. Frequency of Pornography Use and Sexual Health Outcomes in Sweden: Analysis of a National Probability Survey. J Sex Med 2021;XX:XXX–XXX. Sep 12 2021.


Background: Little is known about pornography use and its relationship with sexual health outcomes in the general population.

Aim: To assess frequency of pornography use and the association of sexual health outcomes with frequent pornography use in Sweden.

Methods: Cross-sectional analysis of 14,135 participants (6,169 men and 7,966 women) aged 16–84 years in a Swedish nationally representative survey from 2017. We used logistic regression to assess the association of sexual health outcomes with use of pornography ≥3 times/wk.

Outcomes: Frequency of pornography use (never; less than once/mo to 3 times/mo; 1–2 times/wk; 3–5 times/wk; and daily or almost daily) and sexual health outcomes (eg, sexual satisfaction and sexual health problems).

Results: In total, 68.7% of men and 27.0% of women used pornography. Among men aged 16–24 years, 17.2% used pornography daily or almost daily, 24.7% used pornography 3–5 d/wk and 23.7% used pornography 1–2 d/wk. Among women aged 16–24 years, the proportions were 1.2% for daily or almost daily, 3.1% for 3–5 times/wk, and 8.6% for 1–2 times/wk. Frequency of pornography use decreased with age among both men and women. While 22.6% of all men and 15.4% of all women reported that their or a sex partner's pornography use predominantly had positive effects on their sex life, 4.7% of men and 4.0% of women reported that the effects were predominantly negative. Variables indicating sexual dissatisfaction and sexual health problems were associated with use of pornography ≥3 times/wk: for example, dissatisfaction with sex life (age-adjusted odds ratio [aOR]: men 2.90 [95% CI 2.40–3.51]; women 1.85 [95% CI 1.09–3.16]), not having sex in the preferred way (aOR: men 2.48 [95% CI 1.92–3.20]; women 3.59 [95% CI 2.00–6.42]) and erection problems (aOR: men 2.18 [95% CI 1.73–2.76]).

Clinical Implications: While frequent pornography use is common, potential effects on sexual health outcomes are likely to differ between individuals.

Strength & Limitations: We used a large and recent nationally representative survey with detailed information regarding frequency of pornography use. The temporality of associations of sexual health variables with frequency of pornography use could not be assessed.

Conclusion: In this analysis of a nationally representative survey in Sweden, we found that frequent pornography use was common among young men; that reporting predominantly positive effects of pornography use on the sex life was more common than reporting predominantly negative effects; and that sexual dissatisfaction and sexual health problems were associated with using pornography ≥3 times/wk.

Key Words: PornographyNational Probability SurveySexual Health OutcomesSexual SatisfactionSexual Dysfunction

We assessed the frequency of pornography use and its association with sexual health outcomes using a large and nationally representative survey from 2017 in Sweden. In line with data presented in the survey report,33 around 70% of men and 30% of women aged 16–84 years used pornography; the frequency was higher in younger age groups and decreased with age. Among men aged 16–24 years, approximately 40% used pornography at least 3 times per week (of which around half used pornography daily or almost daily), and over 20% used pornography 1–2 times/wk. Among women in the same age group approximately 4% used pornography at least 3 times per week and 9% used pornography 1-2 times/wk. While less than 5% of men and women reported that their or a sex partner's pornography use had predominantly negative effects on the sex life, over 20% of men and 15% of women reported predominantly positive effects. Dissatisfaction with the quality and quantity of sexual activity and (especially among men) sexual health problems were associated with using pornography 3 times per week or more.

Data on frequent pornography use have been scarce as most studies have used small online surveys or self-selected samples and published data from population-based surveys have not included fine grained information about the frequency of pornography use.26,28,31,32 Data on weekly or monthly pornography use have been presented for 2 US nationally representative surveys from the past decade, although these surveys have not focused on sexual health outcomes. In the Relationship in America survey from 2014, 40% of men and 19% of women aged 18-23 years had used pornography in the past week.30 In the New Family Structures Study from 2011 to 2012, 47% of men and 21% of women aged 18–23 years reported using pornography once a month or more.30 While more detailed data were not presented for these US surveys, weekly pornography use in our Swedish study vs the Relationship in America survey was more common among young men and less common among young women. While it is possible that pornography use differs between the populations, there may be differences between the surveys in the type of individuals who participated and in how they reported their pornography use. Moreover, our study used more recent data (from 2017) and use of smartphone devices and the availability of online entertainment have increased rapidly in the past years.

In accordance with previous research,10,26,38 we found that a minority of individuals reported that their or a sex partner's pornography use had predominantly negative effects on their sex life and reporting of predominantly positive effects was substantially more common. Importantly, frequent pornography use has been subject to much societal concern due to suggested effects on sexual wellbeing and sexual health problems although the evidence regarding such claims is conflicting.2,101112131415,27 We found associations of frequent pornography use with dissatisfaction with the quantity and quality of sexual activity and among men, with lack of arousal when having sex and erection problems. Moreover, we observed an association between frequent pornography use and not having had sex in the last year among men (which was in contrast with previous studies26,39), but not women. Further, while frequent pornography use was associated with reporting predominantly positive effects on the sex life among both men and women, an association with reporting predominantly negative effects was only observed for men; this is in line with previous observations indicating that self-reported problematic use of pornography is more common among men.

Use of pornography has been associated with changes in behaviors during sexual activity29,40 and it has been hypothesized that frequent pornography use introduces dissatisfaction by affecting expectations on sexual activity.41,42 Moreover, pornography use has been suggested to decrease partnered sexual activity and long-term sexual relationships by providing a more easily available substitute.43 However, it is reasonable to hypothesize that sexual dissatisfaction or not being able to find sex partners might increase pornography use.44 Similarly, while frequent pornography use could be hypothesized to increase the risk of sexual health problems, individuals who experience such problems may also use more pornography. The associations could also be explained by other factors (such as stress and boredom45) associated with frequent pornography use and with sexual dissatisfaction, not having partnered sex (among men) and sexual health problems. In fact, erection problems and some variables indicating sexual dissatisfaction were associated with both reporting of predominantly positive and predominantly negative effects of pornography on the sex life, indicating no consistent directionality in the associations of pornography use, as experienced by the respondents, with such outcomes. While the experience of pornography use, its potential effects on sexual health outcomes and the underlying mechanisms for such possible links are likely to differ greatly between individuals, specific sexual interests and type of pornography consumed,21,27 causal effects of pornography use on the group level can only be established in interventional studies. The findings from this study should be considered as hypothesis generating.


We used survey data, which are subject to response and reporting bias,30,46 although such biases might have been mitigated by the use of self-administered questionnaires474849 and the weighting of the sample to be representative of the Swedish population with respect to the distribution of gender, age, region, country of birth and educational level. The survey did not define pornography, nor was information available about the type of pornography used and the duration and context of use. The questions used in the survey had not been validated and their interpretation may have differed between participants. Because the data were cross-sectional, we could not assess temporality of the associations of sociodemographic and sexual health variables with the frequency and self-reported effects of pornography use.

Testing Women’s Trust in Other Women and Same-Sex Attracted Males in Three Cultures

Testing Women’s Trust in Other Women and Same-Sex Attracted Males in Three Cultures. Scott W. Semenyna, Francisco R. Gómez Jiménez & Paul L. Vasey. Archives of Sexual Behavior, Sep 8 2021.

Abstract: Heterosexual women trust mating-relevant advice received from gay men more than that received from heterosexual women. This trust is predicated on women’s perception that gay men lack ulterior sexual motives and romantically pursue other gay men. However, this trust may not hold in all cultures. For example, in both Samoa and the Istmo Zapotec of Southern Mexico, women take part in mate competition against feminine same-sex attracted males—referred to as fa’afafine and muxe, respectively—who regularly engage in sexual activity with masculine men. The present studies sought to replicate and extend research on women’s trust in males who are same-sex attracted. Experiments were conducted in Canada, Samoa, and the Istmo Zapotec, with women randomly assigned to consider the likelihood of various mate-poaching behaviors performed by either a rival woman or a same-sex attracted male. In Canada, women were more trusting of cisgender gay men than other women. Similarly, Samoan women were more trusting of fa’afafine than other women. In the Istmo Zapotec, women were equally distrustful of women and feminine muxe gunaa, whereas more masculine muxe nguiiu were rated as more trustworthy than women and muxe gunaa. These results illustrate that women’s trust in same-sex attracted males varies both between and within cultural contexts, perhaps impacted by the relative femininity of the male in question.

Helmholtz Versus Haute Couture: How Horizontal Stripes and Dark Clothes Make You Look Thinner

Helmholtz Versus Haute Couture: How Horizontal Stripes and Dark Clothes Make You Look Thinner. Antonis Koutsoumpis, Elias Economou, Erik van der Burg. Perception, August 16, 2021.

Abstract: In Helmholtz’s illusion, a square with horizontal stripes appears taller than an identical square with vertical stripes. This effect has also been observed in experiments with human stimuli, where a human figure wearing a dress with horizontal stripes appears thinner than a drawing clad in vertical stripes. These findings do not agree with the common belief that clothes with horizontal stripes make someone appear wider, neither do they disentangle whether the horizontal or vertical stripes account for the thinning effect. In the present study, we focused on the effect of horizontal stripes in clothes comparing horizontal stripes against no-stripes (not against vertical; Experiments 1 and 2), using photos of a real-life female model, and controlling for the average luminance of the stripes (Experiment 2). Results showed that horizontal stripes and lower luminance have—independently—a small-to-moderate thinning effect on the perceived size of the body, and the effect is larger when the two variables are combined. In Experiment 3, we further show that the thinning effect due to the luminance of the dress is enhanced when the general background gets darker.

Keywords: size perception, horizontal stripes, luminance, Helmholtz illusion, clothes

In the present study, we focused on the perceptual effect of horizontal stripes in clothes. Unlike most previous studies, we compared the effect of horizontal stripes against non-striped stimuli, that is, against a neutral condition. In Experiment 1, we found that participants perceived a striped dress (with light-green and black stripes) to be significantly thinner than an identical non-striped (light-green) version of the same dress, but not when compared to a non-striped black version. Since the thinning effect was significant only when the striped dress was compared to the light-green dress, we hypothesized that luminance might moderate the thinning effect. In Experiment 2, we dissociated the stripes and luminance effects by including two extra stimuli. In this way, it was possible to measure the effect of horizontal stripes and luminance on the perceived body width independently, as well as their aggregating effect. The results showed that, first, when the effect of luminance was controlled for, horizontal stripes had a thinning effect against non-striped stimuli. Second, when the effect of horizontal stripes was controlled for, stimuli with lower luminance had a thinning effect against stimuli with higher luminance, either when both stimuli were striped or non-striped. Third, when both stripes and luminance were taken together, the effect was even larger.

Although it seems that the stripes effect holds when the luminance of the stimuli and the background are held constant, the luminance of the background—against which the stimuli were placed—might have affected the thinning effect of darker stimuli. This is because, in the luminance effect, the darker (vs. lighter) stimuli were further away from the luminance of the background and this luminance difference might have affected size perception. In Experiment 3, we manipulated the background luminance (i.e., creating light, average, and dark backgrounds) to investigate whether the luminance effect of Experiment 2 was due to the increased contrast between the dark dresses and the light-grey background. The results showed that the thinning effect of dark dresses could not be attributed to stimuli-background contrast. Instead, we discovered that when the luminance of the general background is darker, the thinning effect becomes more pronounced.

The thinning effect of low luminance is in line with the irradiation illusion (Helmholtz, 1962), according to which a bright area seems larger than a darker area of similar size (Long & Murtagh, 1984Oyama & Nanri, 1960), an effect attributable to the non-linear visual processing of dark and light both on retinal (Valeton & van Norren, 1983Westheimer, 2008) and cortical level (Kremkow et al., 2014). On the cortical level for instance, Kremkow et al. (2014) showed that the ON and OFF neurons operate in dissimilar ways in our visual system, with the OFF neurons responding linearly to external stimuli, and the ON neurons responding in a curvilinear way (overresponding even to limited external stimulation). The practical implication is that dark stimuli are perceived as smaller than bright, not because the size of dark stimuli is underestimated, but rather because the size of bright stimuli is overestimated. As a consequence, the darker dresses in Experiments 2 and 3 were perceived as thinner presumably because participants might have overestimated the size of the brighter dresses.

So far only one study has tested the perceptual effect of horizontal stripes against non-striped stimuli. Thompson and Mikellidou (2011; Experiment 3) found that a cylinder with horizontal stripes was perceived as similar in size (neither wider nor thinner) to an identical non-striped cylinder. This finding is at odds with the results of the present experiments. Nevertheless, the present results suggest that the thinning effect of horizontal stripes seems to be consistent and strong (in terms of effect size and observed statistical power). They also suggest that the thinning effect is further decomposed into two separate effects, that is, both the orientation and the luminance of the stripes affected the perceived size of the dress, and the thinning effect of luminance was further amplified as the luminance of the background decreased.

Our results also extend and partially explain the Helmholtz illusion. In the original paradigm, a square with horizontal stripes is compared to a similar square with vertical stripes. In that context, the thinning effect of horizontal stripes cannot be attributed to luminance, since both stimuli have the same luminance regardless of stripe orientation. It can be attributed, however, to the thinning effect of horizontal stripes, as Experiment 2 showed. Whether vertical stripes also contribute to the overall effect or not, remains an open empirical question.

Future Research

The present results open two main venues for future research. The first is to further probe the boundary conditions that might account for the effect. In the present study we tested the effect of horizontal stripes, luminance, and contrast but the list of confounding variables may be longer. Some variables that might account for the effect include the orientation of the stripes (e.g., test the effect of vertical stripes against a neutral condition), their spatial frequency (the thickness of the stripes), or color. Moreover, previous studies reported that the body size moderates the effect, with bigger body types decreasing (Ashida et al., 2013) or even reversing the thinning effect of horizontal stripes (Imai, 1982). Future studies can test the effect in different body sizes and body shapes (e.g., hourglass, spoon, rectangle).

The second line of research calls for an interdisciplinary approach between the fields of social cognition (participants’ previous beliefs) and psychophysics (participants’ perception). It is striking that, although the results of the present experiments support the thinning effect of horizontal stripes, this finding clashes with participants’ beliefs and leads to a paradox: during the behavioral task in the lab participants perceived horizontal stripes in clothes as thinner, but in self-reports they stated the opposite.3 This inconsistency was also described by Ridgway et al. (2017) where they scanned the body of 15 women and their 3D avatars were presented on a computer. The avatars were dressed in horizontal stripes (and seven more optical illusions) and participants were asked to evaluate them. A thematic analysis (a qualitative in-depth interview method) revealed that a number of participants swayed away from their original negative attitude towards horizontal stripes once they saw themselves in the horizontally striped dress. Although the results of that study were based on qualitative analysis and did not provide any conclusive evidence, the discrepancy between previous beliefs and behavioral responses regarding the effect of horizontal stripes in clothes still remains.

Especially with the increasing devaluation of the other group, but also with the increasing conviction of their own position, the supporters of COVID restrictions accept restrictions regarding the others’ freedom of expression

Polarisation and Silencing others During the Covid-19 Pandemic in Germany: An Experimental Study Using Algorithmically Curated Online Environments. Tim Neumann, Ole Kelm, Marco Dohle. Javnost - The Public, Sep 10 2021.

Abstract: In 2020, societies debated the use of government restrictions on public life to stem the COVID-19 pandemic. Many of these debates took place online. The Internet enables people to come into contact with like-minded content. Algorithms based on collaborative filtering can contribute to this process and might lead to homogenous like-minded online environments that contribute to a polarisation of society. This article therefore examines the effects of (1) like-minded versus opposing online environments, which were (2) randomly versus algorithmically curated. Data from a between-subject experiment embedded in a two-wave panel survey of German citizens (n = 318) show that attitude polarisation as well as affective polarisation are largely independent of exposure to different online environments. Moreover, the results indicate that polarised attitudes of supporters and opponents of the COVID-19-related restrictions relate to varying degrees of beliefs in the importance of silencing people with opposing opinions: While supporters’ polarised attitudes are positively related to the belief in the importance of silencing others, opponents’ polarised attitudes are rather negatively related to such beliefs.

KEYWORDS: belief in the importance of silencing otherscollaborative filteringexperimentonline discussionpolarisationselective exposure


One central aim of this article was to examine the effects of homogenous and algorithmically curated opinion environments on polarisation in the context of the COVID-19 pandemic. For this purpose, data from a two-wave panel survey conducted among the German population with an embedded between-subject experiment were analysed. Participants were assigned to different online environments, in which they were exposed to either (1) like-minded or (2) opposing arguments for restrictions to combat the COVID-19 pandemic. The selection of these arguments was either (1) random or (2) based on an algorithm with collaborative filtering.

The results show that the generated online environments did not influence attitude polarisation, i.e. they did not affect how certain the respondents are in terms of their respective attitudes toward the government actions. One reason for this could be that the COVID-19 pandemic is not the ideal context to test the influence of like-minded online environments and the role of algorithms as, for example, many people are most likely confronted with information on this topic outside online environments (Viehmann, Ziegele, and Quiring 2020). This potentially limits at least the short-term effects of arguments presented in online environments. Moreover, the non-existent effects regarding the selection mode must be treated with caution, as the manipulation check regarding the selection mode failed.

Another reason could be that the respondents’ attitudes toward the government actions were so pronounced that they could not even be strongly influenced by the presentation of convincing arguments. However, other explanations for these non-existent effects are possible. For example, it might not only be the content of an argument that is crucial to its persuasiveness. Instead, also in algorithmically curated online environments, how an argument is presented and whether, for example, it is presented factually, emotionally or embedded in a narrative might be (more) relevant. Even more obvious, who has authored and spread the argument might also be important. In line with the echo chamber hypothesis, other people echo one’s own opinion. Through repeated interaction, people can build a relationship with these like-minded others, giving their arguments more weight than the arguments of other people or, which seems to be relevant in the case at hand, than the arguments that are presented via an anonymous platform. In addition, people more often use the content of sources and people they trust (e.g. Strömbäck et al. 2020). As a result, and in line with the filter bubble hypothesis, algorithms with collaborative filtering are likely to select more often information from these sources or from people with whom the people in question more often interact. Thus, the impact of the authors of the arguments, which did not play a role in the presented experimental study, may be crucial.

The experimental results also show that the different online environments created in this study did not influence affective polarisation. Again, the reason could be that the respondents’ attitudes toward the other group were so pronounced that they could not be strongly influenced by the content presented via the online discussion platform. However, it might also be the case that group identification in the context of the COVID-19 pandemic is too low. Many people in Germany had an opinion on the government actions, but they might not have seen themselves as part of a specific group—maybe also because they recognised that (almost) the entire population was and is affected by the consequences. This makes affective polarisation as a consequence of arguments that were presented only once more unlikely. More likely, affective polarisation may occur as a consequence of observing behaviour that one disapproves of (e.g. ignoring restrictions on demonstrations). Another explanation is that the presented arguments were within the democratic spectrum of opinion and did not contain, for example, incivility, exaggeration or satirical elements. These elements may trigger affective polarisation more strongly than the direction of an argument (Druckman et al. 2019).

Another central aim of the study was to examine how attitude polarisation and affective polarisation are related to the BISO. The study shows that affective polarisation among the opponents of restrictions is rather negatively related to the BISO. In view of previous research results (Tsfati 2020), this may initially be surprising. However, it is conceivable that the opponents of the restrictions consider the restrictions as an unreasonable limitation of their fundamental rights. Since they perceive their fundamental rights as already being restricted, they might fear further restrictions of such rights. If they themselves silence other groups, this will lead to cognitive dissonance, which they want to avoid. Moreover, as there are no short-term political majorities for their demands, they are, compared to the supporters of restrictions, more dependent on a public debate that is as open and broad as possible.

For supporters of the COVID-19-related restrictions, however, the results were different: Especially with the increasing devaluation of the other group, but also with the increasing conviction of their own position, the supporters of restrictions want to prevent positions perceived as dangerous from being spread—for this reason, they also accept restrictions regarding the others’ freedom of expression. The differences between the supporters and the opponents of the restrictions can also be explained by the object of silencing: Tsfati and Dvir-Gvirsman’s (2018) understanding of the BISO focuses on interpersonal communication—whether face-to-face or in online environments. From the point of view of the opponents, there are reasons to support a broad public debate (which, of course, includes all forms of interpersonal communication), whereas from the point of view of the supporters of the restrictions, there are reasons to limit this public debate to acceptable contributions. If silencing had been applied to journalism or authorities, the results might have been different.

The study has limitations. Although government restrictions and incidence numbers in Germany changed little during the fieldwork, many people’s opinions toward the restrictions changed. The results of the control group of this study also illustrate this: In total, 21.9 per cent of the respondents assigned to the control group changed their opinion toward the restrictions from t1 to t2. Thus, the time gap between t1 and t2 may be responsible for the fact that arguments selected by the algorithm were not (more) convincing. This also became apparent in the manipulation check, which did not show a significant difference in the persuasiveness of the arguments that were randomly selected and those that were selected by the algorithm.

Second, the respondents were only briefly exposed to the stimulus. This may have reduced its effects. This might be especially true for the chosen topic, about which most people have probably received extensive information via many sources. Further studies should examine the effects of different online environments in other polarised contexts that are less in the media spotlight (e.g. genetically modified food).

Third, the respondents were not able to choose which online environment they entered (“forced exposure”), and forced and self-selective exposure might have different effects on polarisation (e.g. Arceneaux and Johnson 2013).

Fourth, as the results of the regressions are based on cross-sectional data, no causal claims can be made, which is why no mediation models were calculated (see Chan, Hu, and Mak 2020), even if the results suggest potential mediation effects. The results imply that attitude polarisation has an effect on the BISO and that this effect is mediated by affective polarisation. To test these assumptions, experimental studies should (1) manipulate attitude polarisation to analyse its potential effect on affective polarisation and the BISO and (2) manipulate affective polarisation to analyse its potential effect on the BISO.

Finally, we only focused on one country. Thus, it is unclear whether the results are generalisable to other contexts.

Despite these limitations, the present study contributes to current research on how like-minded and opposing online environments influence polarisation. Even though it cannot be ruled out that the non-existent findings are due to the experimental set-up, it is also possible that the results indicate that the process of how like-minded or opposing information influences polarisation is more complex than previously suspected. More studies are needed that focus on the potential effects of being exposed to these online environments. Experimental studies using algorithmically curated stimuli may be helpful to determine the effects. Furthermore, this study has shown that the BISO is a theoretical concept that is also relevant in more (national) contexts than those previously tested (e.g. Tsfati 2020). Silencing others and the belief in the importance of doing so may be important concepts for understanding polarised societies.

Sex differences in total brain volume are not accounted for by sex differences in height and weight, and that once global brain size is taken into account, there remain numerous regional sex differences in both directions

Sex differences in the brain are not reduced to differences in body size. Camille Michèle et al. Neuroscience & Biobehavioral Reviews, September 11 2021.

Abstract: In their comprehensive review of sex differences in the brain, Eliot et al. (2021) conclude that (1) men and women significantly differ in global brain size, but this “mostly parallels the divergence of male/female body size during development” and that (2) “once we account for individual differences in brain size, there is almost no difference in the volume of specific cortical or subcortical structures between men and women”. In sum, almost all brain differences would directly or indirectly follow from differences in body size. In a recent study that does not have the same limitations as most studies reviewed by Eliot et al., we find that sex differences in total brain volume are not accounted for by sex differences in height and weight, and that once global brain size is taken into account, there remain numerous regional sex differences in both directions (Williams et al., 2021).

Keywords: sex differencesBrain VolumesCortical Mean ThicknessesCortical Surface Areas