The current study employed a top-down triangulation approach utilising several methods simultaneously to describe different approaches to studying affective responses and their physiological significance. To point out the main differences again, explicit ratings are behavioural measures which require a conscious, deliberate response and therefore utilise cortical information processing. Startle Reflex modulation is a non-conscious measure of raw affective information processing on the basis of motivational priming (see [57
]) and relates to subcortical brain structures, e.g., [29
]. Electroencephalography (and further to that, ERP) is mainly sensitive to cortical information processing, but it also involves the coordinated input from sub-cortical brain (largely non-conscious) processes. It can be said that all physiological measures are rather implicit by nature in contrast to explicit rating performance.
With this knowledge in tow, can we determine if the frequency of pornography use alters the way in which we consciously (explicit measures) and non-consciously (implicit measures) respond to emotional information? Although the Snyder scores for each group did not differ significantly—indicating no difference in self-monitoring—the results obtained in the current study indeed demonstrated discrepancies in the results obtained via explicit and implicit measures.
4.2. Event-Related Potentials (ERPs)
Notable significant differences were observed between the “unpleasant” relative to the “violent” condition between groups, which is in contrast to explicit rating results. Upon visual inspection of the curves, an increased negative peak can be seen in the low porn use group for the “unpleasant” condition during the LPP phase of the curve (400–500 ms) across both hemispheres in frontal areas of the brain. This appears to only be present in the right hemisphere for the medium and high porn use groups. Although this laterality effect did not survive statistical analysis, the trend observed could indicate a possible lateralisation effect of more frequent porn users. This prominent negative peak was also demonstrated by a study performed by Cuthbert et al. [59
], where they found that frontal areas of the brain showed greater positivity for pleasant than unpleasant pictures albeit, the “neutral” condition in their study was the most negative going. The authors of the aforementioned paper attempted to make sense of this relative positive shift of pleasant images by stating that it could reflect augmented affective arousal rather than an intrinsic valence difference due to the pleasant images in their study evoking a significantly greater change in autonomic activity (skin conductance) rather than subjective arousal ratings. In addition, this pattern of frontal asymmetry can be explained by the relative positive going waveform the “unpleasant” images produced in the left hemisphere of the medium and high porn use groups. Recent research suggests that increased relative left frontal activity may be associated with approach motivational processes (see [60
]). This would indicate that due to the relative frontal difference in activation to the “unpleasant” images, more frequent users of pornography possibly consider the unpleasant images to contain more positive affect.
Furthermore, the “violent” and “unpleasant” emotion categories across the right hemisphere appear to increasingly follow a similar trajectory at slightly later time periods (>500 ms) moving from low to medium to high porn users—particularly in the frontal region of the brain. These findings suggest that similar processing may be utilised by frequent users of pornography when passively viewing violent and unpleasant emotion images relative to lower pornography users at implicit levels. Heading more posteriorly to more sensory-related areas of the brain, the same two emotion categories (“violent” and “unpleasant”), again, appear to be processed more similarly in the high porn use group during the LPP phase (>500 ms) where they remain separate in the low and medium use groups. This pattern of physiological responses may suggest that frequent exposure to pornographic material may increase the liking and therefore approach motivation towards that stimulus, thereby resulting in an enlarged LPP comparable to the LPP generated due to the possible avoidance motivation resulting from viewing violent imagery. Contrastingly, as mentioned above, it has been shown that many frequent users of pornography often gravitate towards more graphic or intense material over time due to desensitisation effects and the need to view more novel and extreme material to become aroused [58
]. This material may often include pornographic genres which depict varying acts of (sexual) violence which individuals in the high use group may be primed to and therefore respond to the “erotic” images on a physiological level similarly to the “violent” images.
4.3. Startle Reflex Modulation (SRM)
Startle reflex modulation, as mentioned previously, is sensitive to subcortical affective processing with a clear emphasis on valence. As expected, results showed the “erotic” category to be the least startle-inducing, and across all three groups, the “violent” emotion category elicited the largest startle response. Although results obtained showed a p
-value only approaching significance, upon visual inspection of the curves it can be seen that there are three distinct profiles of startle responses characteristic to each group. A trend is visible moving from low to medium to high pornography use, as the relative distribution of startle responses appear to increase in variability (i.e., the high porn use group has the biggest range of startle responses between the least arousing (erotic) and the most arousing (violent) emotion categories). This indicates that higher frequency porn users process the “erotic” images as more appetitive in relation to the other emotion categories on a non-conscious level (however, only qualitatively). The observed effect seems to be in adherence to most studies in this field, whereby startle reflex to aversive stimuli result in higher amplitude blink responses compared to more pleasant stimuli [32
]. A possible explanation as to why the high porn use group showed a relative decrease in startle response to the erotic images may be due to all the images presented more than likely being novel to the participants and therefore their affective non-conscious startle response indicated that it was a pleasant stimulus which had not proceeded to habituation. As it is so, it would be interesting to determine what effect repeated viewing of the same images may have, as previous studies have shown repeated viewing of erotica results in increased eye blink response to a startle probe due to the material becoming boring and aversive [41
]. The relative higher amplitude startle effect seen in the low and medium porn use groups may be explained by those in the group intentionally avoiding the use of pornography, as they may find it to be relatively more unpleasant. Alternatively, the results obtained also may be due to a habituation effect, whereby individuals in these groups do watch more pornography than they explicitly stated—possibly due to reasons of embarrassment among others, as habituation effects have been shown to increase startle eye blink responses [41
Although the significance level obtained may not be what was expected, a trend seems to be emerging from the data showing the discrepancy between frequent and infrequent pornography users. It is of the authors’ view that the lack of a concrete result may be attributed to low participant numbers. A larger cohort would more than likely increase power to detect more robust effects. However, it appears that the observed trend in physiological data of the current study provides another pattern of findings dissimilar to explicit ratings.
Although the current study was comprehensive, there remained inevitable limitations. It should be mentioned that the images which formed the “erotic” category obtained via the IAPS database may be seen as an outdated representation of erotica or pornography compared with what may be construed as “average pornography” which, in the modern era, is more expansive and visually stimulating. Future studies may need to utilise a more up-to-date standardised image database to account for changing cultures. Also, maybe high porn users downregulated their sexual responses during the study. This explanation was at least used by [7
] to describe their results which showed a weaker approach motivation indexed by smaller LPP (late positive potential) amplitude to erotic images by individuals reporting uncontrollable pornography use. LPP amplitudes have been shown to decrease upon intentional downregulation [62
]. Therefore, an inhibited LPP to erotic images may account for lack of significant effects found in the present study across groups for the “erotic” condition. This may be due to participants not being allowed to masturbate whilst watching pornographic (or in this case, erotic) images during the testing session, which is what they may do otherwise [64
A further limitation of the current study was that the participant pool was divided into pornography use groups based on self-reported pornography usage. As studies based on physiology in this field of pornography consumption is relatively recent, there does not yet exist a set of physiological markers or a physiological profile which allows for a clear distinction between, say, a “low” or a “high” pornography use group. The obvious issue presented with this method may be due to some respondents’ under-reporting or over-reporting their actual porn use. Further, the current study did not rely on a clinical sample with known and clinically diagnosed pornography use problems. The cohort used for the present study exists within a “normal” range with unproblematic porn use which may be termed not clinically significant and therefore may not have provided as robust a result as a comparison between clinically diagnosed and non-clinically diagnosed individuals.
Furthermore, the effects noted in this paper differentiating between pornography use groups may indicate a correlation effect rather than causation. A link may be drawn here comparing individuals in the general population who consume alcohol. Both pornography consumption and alcohol use may be pleasurable and potentially damaging behaviours engaged in by many, but only a minority of individuals excessively participate in these behaviours to the point where it causes distress and associated adverse behavioural effects. It is entirely likely that our cohort was comprised of individuals who have not and will never suffer any sort of observable adverse behavioural effect due to their (excessive) use of pornography.
The study of excessive pornography use is a relatively recent phenomenon, and there is a need to develop a standardised questionnaire used to explicitly measure pornography use and its associated conscious effects. There exist several already established scales and measures used to determine various aspects of sexual behaviour, among them: the Sexual Compulsivity Scale [65
], the Pornography Craving Questionnaire [66
], the Pornography Consumption Effects Scale [67
], and the Problematic Pornography Use Scale [68
], but with the quickly changing nature of individuals’ pornography acquisition via the internet and what is available on it, many of the items on these scales may be seen as obsolete and need to be updated, but due to the lack of an existing, well-validated and psychometrically sound measure many studies (as we have done) have opted to develop and use their own in-house, purpose-built and developed items and methods of scoring whilst others (especially those studying pornography addiction) have simply resorted to adapting existing substance addiction scales and substituted the addictive substance (e.g., alcohol, cocaine, heroin, etc.) with the word pornography. The problem with this is a lack of reproducibility and validity of the measure to acquire consistent and accurate results among studies in this field.
In summary, although all measures showed significant (or close to significant) outcomes, it is important to note that differences observed in the explicit ratings were not the differences observed in the physiological measures. Similar to word information processing where a dissociation was found between explicit and implicit responses (see [69
]) this indicates that there are definitely grounds to conclude that as there are differences in the way affective information is processed both consciously and non-consciously, no single method of measurement can provide an accurate description of an individuals’ true emotional state. In saying so, multiple standardised methods incorporating both implicit and explicit measurement techniques may need to be utilised in order to gauge all different aspects of affective processing leading to emotions. Surely, a survey alone does not lead to solid results.