Visual Exploration in Adults: Habituation, Mere Exposure, Or Optimal Level Of Arousal? Part 3

Results

The mean proportion of looking time towards novelty, according to the type of image and familiarization length, is presented in Fig. 3. The interaction between the type of image and familiarization length did not reach significance, F(1, 45) = 0.679, p = .410, ηp 2 = 0.001. 

There is a strong link between image type and memory, with positive image types helping to improve memory.

First, image type refers to image information composed of visual elements. These image information enter the brain through the visual channel and are processed. Compared with text information or language information, image information is easier for the brain to process and remember. Therefore, converting information into image types can better facilitate memory formation.

Secondly, positive image types can stimulate people's memory abilities. For example, image types such as beautiful natural scenery or cute animals can bring pleasant feelings and make people's memories more profound. Conversely, negative image types may bring out negative emotions in people and hinder memory formation.

Finally, image type can improve memory persistence. Because image types are easily processed and remembered by the brain, they remain in people's memories longer. If we convert the information into image types and use the right way to memorize it, it will be easier for us to remember the information in the long term.

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No effect of the type of image was observed, F(1, 45) = 1.137, p = .287, ηp 2 = 0.001. The length of familiarization had a significant effect on the proportion of time looking towards novelty, with relatively longer looking time after a long familiarization compared with a shorter one F(1, 45) = 13.239, p < .001, ηp 2 = 0.014. 

We also compared the proportion of novelty-looking to chance with one-sample t-tests. After a short familiarization, participants did not look at novel flowers, t(23) = 1.355, p = .189, or fractals, t(21) = −0.905, p = .376, more than would be expected by chance. 

However, following long familiarization, participants were significantly more likely to look at novel flowers, t(21) = 4.038, p = .001, and fractals, t(23) = 3.266, p = .003, than would be expected from chance.

Subjective preference

Results from LME models are summarized in Table 2. Family familiarity tended to affect participants' attitudes toward the stimuli. Indeed, pairwise comparisons showed that ratings tended to be more positive for semi-familiar families (M = 5.652 ± 1.955) compared with familiar ones (M = 5.282 ± 1.865, p = .086). 

Although that effect was not significant, the interaction between family familiarity and image novelty was a potentially important factor affecting ratings. 

Further analyses on "already seen" and "novel" images separately showed that, for "already seen" images, semi-familiar families had significantly higher ratings (M = 5.899 ± 1.923) compared with the familiar ones (M = 5.065 ± 1.948, χ2 1 =7.327, p = .007). 

In contrast, family familiarity did not affect "novel" images (χ2 2 = 0.061, p = .97).

Discussion

The findings of this study concerning exploratory behaviors and subjective evaluations in adults generally support the predictions of the optimal level, the two-factor, and the dual-process models. How the models fare about the research hypotheses is summarized in Table 3. 

The first goal of this study was to determine if, for adults, the level of habituation influences visual exploration behavior toward a stimulus. More specifically, the aim was to ascertain whether, as with babies, short habituation is associated with visual exploration towards familiarity, whereas longer habituation leads to an exploration towards novelty. 

Indeed, we found that the gaze was more oriented towards novelty after a long exposure, which is in line with the predictions of the optimal level and the two-factor model. However, short familiarization did not bias orientation towards either novelty or familiarity. 

It is possible that participants were transitioning from a visual exploration of familiarity to a visual exploration of novelty, but our method did not allow us to assess this possibility. 

There is a temporally limited window for observing orientation biased towards familiarity, and our short familiarization may have been too long to observe it. This could have been avoided by using a participant-controlled habituation paradigm, where the number of exposures would have been controlled by eye-tracker data and would have depended on the decline in looking time for each participant (Aslin, 2007). 

We cannot conclude that adults tend to look more at familiar stimuli until habituation is reached, but we can conclude that, with longer exposure, adults tend to explore new stimuli. The pattern of findings is consistent with what has been noted in human infants (Sirois & Mareschal, 2004).

The second goal was to evaluate the influence of habituation on participants' subjective evaluation of the stimuli, and if that evaluation would follow the predictions made by the optimal level of arousal and the two-factor model of mere exposure. 

Interestingly, semi-familiar families received a higher rating than familiar families. This is in line with the predictions of the optimal level of arousal and the two-factor model of mere exposure, stating that a positive attitude should appear only once a particular level of arousal, or novelty, is reached. Since this effect of familiarity was only marginally significant, this finding should be approached with caution. 

However, in a similar vein, semi-familiar families received the highest ratings when participants were viewing already-seen images. This is again in line with the optimal level of arousal and the two-factor model of mere exposure. Interestingly, a recent meta-analysis suggests that the mere exposure effect could be an artifact appearing when a sufficiently high level of familiarization is not reached (Montoya et al., 2017). 

Thus, orientation towards novelty after familiarization could be a means to get closer to one's optimal level of arousal, in line with the theory of the same name. Such orientation could then also be an artifact appearing, this time when an excessive level of familiarization is reached. Novelty, along with complexity, intensity, salience, or affective content, is a determinant of arousal (Bradley, 2009; Calvo et al., 2007; Faw & Nunnally, 1968; Ronga et al., 2012). 

Future studies could disentangle the effect of the optimal level of arousal (or stimulation) model and the two-factor model of mere exposure by taking the physiological measures of participants and seeing whether their preferences correlate with their physiological arousal level, and how these measures would fit with the inverted-U shaped characteristic of both models. As we did not control for image luminance in our study, our data were not appropriate for pupillometry analyses. 

Future studies replicating these first results would benefit from a design that allows for pupillometry as an objective measure of arousal (Laeng et al., 2012). It is also worth noting that habituation is generally slower for affective stimuli than for neutral ones (Bradley, 2009; Carretié et al., 2003). 

Moreover, the affective value of stimuli facilitates engagement and impairs disengagement (Machado-Pinheiro et al., 2013; Nummenmaa et al., 2006) and has been found to influence the mere exposure effect (Courbet, 2003; Jin & Luo, 2011). 

Although some participants may have attributed an emotional valence to the flowers or the fractals (Rogowitz & Voss, 1990), the images we used were globally considered mostly neutral (ratings slightly higher than 5 on a 9-point scale). It is possible that in previous studies, a positive attitude towards the stimuli could have compensated for excessive familiarization resulting in a mere exposure effect. 

Altogether our study has shown that relatively long familiarization favors the exploration of novel visual stimuli, in line with previous works on habituation effects. That said, adults show a more positive attitude towards semi-familiar stimuli compared with very familiar or very novel ones, in line with the optimal level of arousal and the two-factor models. 

This study is the first to show evidence supporting both phenomena using the same set of stimuli and number of presentations, and using different dependent measures (preferential looking and subjective preference). Future neurophysiological studies may help disentangle the role of arousal and cognitive load in determining such preferences.

Acknowledgments We are grateful to Pierre-Olivier Parisé for his help in creating the fractal images. This research was supported by an Undergraduate Student Research Award to the second author from the Natural Sciences and Engineering Research Council of Canada (NSERC), and funding from the Canada Research Chairs program (through NSERC) to the last author.

Data availability Data and materials have been made available online in an open repository (https://doi.org/10.17029/b5320d45-e55f-47e9-8e81- 8b76a6876f1e). This study was not preregistered.

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