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The Effects of Faces and Emotional Expression on Binocular Rivalry
Faces are considered to be a unique source of information that provide identification of emotional states, intentions and physical characteristics. Therefore, facial perception is considered to be an essential aspect of human cognition (Wilmer et al. 2010). The processing of faces occurs in the localised intra-hemispheric structures such as the fusiform gyrus and is important for visual perception (Iaria et al., 2008). Binocular rivalry occurs when two conflicting images fall on both eyes and they compete for dominance due to the inability to merge into a single image (Alpers and Gerdes, 2007). This results in the individual observing both images separately for a couple of seconds until ultimately, one image dominates over the other (Tong, 2001). It has been suggested that the fluctuations between the two images are not a part of conscious control. Only in recent years has research extensively focused on the impact of binocular rivalry on visual perception. Blake (2001) explains that the dominance or suppression of the images is established only after both of the monocular visuals are evaluated. Claims have been made that the assets of the two stimuli are processed separately within their designated areas of the brain before one image wins and extents to conscious responsiveness (Logothetis et al., 1996). Some influences on the dominance and suppression phases of binocular rivalry include attention, context, motion and spatial frequency. However, the impact of the stimulus’s emotional matter also has been suggested to accelerate visual dominance.
An experiment conducted by Engel (1956), conveyed that images of upright faces which were well-known and emotional conquered images of inverted faces. This experiment had many limitations however, similar results were presented in Yu and Blakes (1992) well established study. It has been proven that humans have a limited ability to process all incoming information that is available at one point. Therefore, Ohman and Mineka (2001), explain that it would be useful for visual priority to be given to meaningful stimuli because it provides an opportunity for the observer to react quicker if they placed in a dangerous situation. Lundquvist and Ohman (2005) investigated emotional expression by using visual search models and found that negative facial expressions were identified faster than neutral or positive facial expressions. The dot-probe experiment, also demonstrated similar results as detection was accelerated when an angry expression was presented after the probe, rather than when followed by a neutral or positive expression (Mogg and Bradley, 1999). Evidence has also shown that emotional expressions are more resistant to breakdowns of attention and insert into awareness rapidly (Fox et al., 2005). Amaral et al. (1992) demonstrated that the amygdala has direct pathways to areas of the V1 and V2 of the visual cortex. Based on this evidence, Alpers and Pauli (2006) suggested that this means that emotional content could dominance over other types of stimuli during visual perception. Coren and Russell (1992), during their study presented participants with different emotional expressions and discovered that happy or angry faces had more of an effect than neutral faces on binocular rivalry. However, the participants were asked to report their observations after the experiment had concluded which may have caused them to report based on memory (Bannerman, Milders, Gelder and Sahraie, 2008). Another experiment conducted by Alpers and Pauli (2006) examined emotional images in comparison to neutral images on binocular rivalry. They found that participants preferred emotional expressions to neutral expressions. However, participants were asked to voice their experience afterwards, which could have been why they reported more emotional expression viewing as a result of reporting-bias. In addition, physical viewing differences such as light and contrast were not measured, and may have contributed to the findings of the study.
This study will attempt to identify whether emotional expression will dominate over neutral faces or other stimulus types. It has been hypothesised that angry faces will dominate over and suppress neutral faces and non-face objects. The independent variables identified are stimulus category (faces or houses) and facial emotion (angry or neutral). The dependent variable is the viewing time of the stimulus types. The aim of this study is to examine whether the face images will dominate visual perception and whether emotional expression matters in binocular rivalry.
Participants in this study included Macquarie University students currently enrolled in COGS202. 76 students (19 male, 57 female) were separated into random groups of three to four by their tutor and asked to conduct the experiment together. COGS202 is a year two unit, which consists of students aged from 19-25 years old. 71 students were right-handed and 5 students were left-handed.
The software used to conduct the experiment was the application Oculus. The Oculus Rift headset and sensors was used to produce the virtual reality conditions that assisted in the experiment for binocular rivalry. The images used in this experiment were an angry face (with teeth showing), a neutral face and house images that were faced front on.
The participants were asked to join their group and open the Oculus application on the desktop. The experiment was available on iLearn, which required students to sign in with their student ID’s and download the relevant application called ‘Binocular Rivarly’. Each participant was asked to complete six trials (3 x 30 seconds for each stimulus type) along with one practice trial prior to beginning. The participant was asked to press the key that corresponds to the dominant image seen and press the space bar if they saw a mixed image. The experimenter was asked to select an image pair by pressing the A and S keys for either pair 1ab or pair 2ab. Pair 1ab was the angry face and house trial, and pair 2ab was the neural face and house trial. The faces and houses presented were all grey-scaled images. They were asked to run the experiment three times, and then change eyes by pressing the Z key to complete another three trials. After the six trials were complete, the data recorder would note down their results in the correct section of the experiment sheet. After all students had conducted the experiment, they were asked to calculate the mean for every participant and input the data into the spread sheet.
Jamovi software was used to analyse the data of the experiment. The experiment’s significance threshold was 5% (< 0.05). The results were automatically adjusted when the multiple t-tests were run on the statistical values. The experiment values are faces and houses.
Results were recorded and analysed through the use of paired sample t-tests. The results were derived from the comparison between angry face/house (pair 1ab) and neural face/house (pair 2ab). In pair 1ab, results depicted a significant inclination for angry faces (M = 11. 60, SD = 5.11) over houses (M = 6.38, SD = 3.50), t(75) = 6.83, p = <.001. In pair 2ab, there was also a significant effect for neutral faces (M = 10.93, SD = 3.48) over houses (M = 5.34, SD = 2.94) t(75) = 9. 19, p = < .001. Figure 1 depicts that detection for neutral faces and angry faces produced similar results, with angry faces showing a slight advantage over neural faces. However, this result was not high enough to be deemed significant (M = 0.66, SD = 4.47) t(75) = 1.28, p = <0.203. These results do not support the proposed hypothesis that angry faces will produce significantly higher results than neural faces, in regards to emotion. However, in Figure 2 when accessing in pairs, pair 2ab (neural faces and houses) produced a slightly higher detection rate than pair 1ab (angry faces and houses). This result was also not high enough to be deemed statistically significant. It does however, support the hypothesis that imply that faces will be dominate visual perception as opposed to non-object stimuli such as houses, as presented in Figure 1.
As mentioned previously, the hypothesis suggested that faces would dominate over non-object stimuli such as houses and that angry faces will produce faster detection rates than neutral faces. The hypothesis was only partially supported as the results lent support to the hypothesis that faces would dominate over houses but excluded the hypothesis that angry faces would produce faster detection rates than neutral faces in binocular rivalry, therefore the null hypothesis could not be rejected.
As anticipated, faces did dominate over non-object images such as houses in the study. Bertolino, Ferraro, Nigri and Ghielmetti et al. (2014) produced similar results and explained that faces, due to their ecological relevance are easier to identify than another one type of stimuli. This provides support to the finding that faces dominated over houses in the experiment. Alais and Melcher (2007) also suggest that the complexity of the image presented is an important factor to consider when investigating the effects of binocular rivalry. Complex stimulus such as houses and faces will only compete with other images that share the same complexity (Alais and Parker 2006). In regards to the study conducted, this allows for a fair evaluation of the stimuli involved in the experiment. Aguirre et al. (1998) also stated that houses and faces are processed in extrastriate areas of the brain that process visual objects. This is thought to play a central role in the organising of rivalry between the two stimuli as mentioned by Lee and Blake (2004).
The findings presented on the impact of emotional expression on binocular rivalry found that angry faces did not produce significantly relevant results in comparison to neural faces. Yu and Blake (1992) revealed different results, by concluding that emotional images such as faces predominate over random visual input such as houses. Hansen and Hansen (1988) and Ohman, Flykt and Esteves (2001) also came to the same conclusion during visual search task experiments. They found that there is increased visual cortex activated when participants are presented with images that produce or convey emotion (see Schupp, Junghoefer, Weike and Hamm, 2003). Historically, this effect has evolved due to humans needing to readily notice expressive cues available. These findings imply that feedback from amydala may cause the high arousal and faster identification of negatively emotional images (Amaral et al., 1992). It has been suggested that due to this, the competitive strength of the emotional images ensures they reach consciousness faster than other types of stimuli.
Several limitations could have interrupted the process of the experiment therefore, affecting the perceived results. The informal setting of the experiment could have hindered the results. The experiment was set in a university classroom with 20-30 other students within the room. This could have affected the data, as the space was loud and noisy and could have diverted the participant’s attention meaning they did not become completely immersed in the experiment. Also, the sample of participants were all young university students who had the unit guide and were aware of the hypothesis the study was attempting to test. This could have yielded bias and unreliable results as many students may have purposely selected the faces as the dominant images. All participants had to partake in being the subject of the experiment, the data collector and the experiment coordinator. Due to this, the participants who performed the task last had previously experienced the task through instructing their team members on how to complete it. This could have hindered the results, as the participant was aware of the experiment’s requirements prior to conducting it. Alternatively, differences in characteristics that relate to binocular rivalry could have played a role in the findings. Contrast and luminance as stated by Blake (2001), have been proven to influence the perception of visual stimuli. Lang et al., (1998) also explained that the complexity of the image plays a crucial role in binocular detection. Due to slight differences in these areas, the results could have displayed bias findings. Future research should be focused on ensuring the participant is in a formal setting with little distraction and the physical characteristics are controlled to ensure that data is reliable.
In sum, this study supports the idea that binocular rivalry is heightened when viewing faces in comparison to houses. However, it could not lent support to the belief that emotion influences binocular rivalry and therefore, further research should be conducted in order to investigate these results and understand whether emotional expression does play a role in faster detection rates between stimuli.
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