4.2.3.1 Introduction
The aim of Experiment 6 was identical to Experiment 4 and 5; to examine the effects of perceptual load on facial judgment detection accuracies; although like Experiment 3 we employ the arguably more emotional stimuli of threatening faces to examine and contrast the effects of perceptual load on facial judgment detection accuracies with the prior results (where participants performed the facial social judgment task before the perceptual load search task).
Once again, given that our prediction is that any impairment in facial social judgments is specific to perceptual load (Lavie et al., 2004) we do not expect that the order of tasks should drastically impact the pattern of results and thus hypothesize a similar pattern observed for threat in Experiment 3, that is, threat judgment accuracies will be reduced under high load.
4.2.3.2 Method
4.2.3.2.1 Participants
15 participants were included in Experiment 6; Mean Age 19.47, SD 1.64 (4 males) (range 18 - 24) (1 outlier removed). All of the participants in this experiment had normal or corrected-to-normal vision, as in the prior experiment, any subject with less than 50 % accuracy on the Low Load face or search tasks was classified as an outlier and removed from the subsequent analyses, participants participated for course credit or were paid £3 pounds.
4.2.3.2.2 Stimuli, Procedure and Design
Once again the apparatus and procedure and design were identical as Experiments 4 and 5, except that the participants were instructed in this instance to make their response on 24 faces identities that vary on 4 levels of threat.
4.2.3.3 Results and Discussion
Search task Mean percentage search accuracy rates were significantly better in the low
perceptual load condition (M = 90 %) than in the high perceptual load condition (M = 80 %), F(1, 14) = 13.81, MSE =.022, p < .005, η2 = .50. There was no significant effect of valence (F<1) F(3, 42) = .63, MSE = .11, p = .597, η2 = .043. Additionally there was no significant interaction between valence and load (F<1) F(3, 42) =.17, MSE =.009, p = .913, η2 = .011. This again confirms that the perceptual load manipulation was effective (see Table 4-3).
Perceptual load
Low High Differential Effect of load
Search Accuracy (%) 90(8) 80(13) 10*
Face Accuracy (%) 78(11) 72(11) 6*
SDs are listed in parenthesis. * = significant NS = not significant
Table 4-3 Mean percentage search accuracy rates and mean face accuracy rates in the reversed threat task as a function of load in Experiment 6
Face classification. Mean percentage threat face accuracy rates in the low perceptual load condition were significantly higher (M = 78 %) than in the high perceptual load condition (M =72 %), F(1, 14) = 11.20, MSE = .009, p = .005, η2 =.44, indicating the effect of perceptual load. There was
again a significant effect of valence F(3, 42) = 9.91, MSE =.044, p < .001, η2 = .41 and a significant interaction between valence and load F(3, 42) = 4.04, MSE = .018, p = .013, η2 = .22.
Figure 4-4 Threat mean percentage face accuracy rates in the task reversed assignment (valence ranges low threat valence -3SD on the left to high threat +3SD on the right)
This result again seem seems cautiously reassuring in that we have replicated the presence of a main effect of load seen in Experiment 3 and the response pattern seen there (Figure 3-6) with a significant effect across the valence range is broadly similar to the one shown above (Figure 4-4). Again there are minor differences between the two; such as here numerically -3SD valence mean accuracy is actually greater under high load than low load.
The significant interaction between load and valence in Experiment 6 also has to be borne in mind (an interaction not present in Experiment 3). Although follow up testing revealed that none of the low load vs. high load pairs were significantly different for any of the categories (-3, -2, +2, +3 SD faces) in Experiment 3, here, the high threat face accuracies for maximum threat +3SD valence were solidly and significantly reduced under high load (t (14) = 5.41, p <.001 (low load M = 85 % vs. high load M = 66 %)). It is this large difference which is driving the interaction between load and valence. On the whole, the pattern seen here for threat broadly coheres in the task reversed assignment with that for threat seen in the prior chapter, although the effect of load was more formidable on high threat faces than that sees in Experiment 3 (in Experiment 3, although +3SD valence faces were the most impacted by high load with a difference of 7.5 % between low and high load, this is more than half of the observed effect here at 19 %). This could imply that for certain judgments, the slight difference in time that occurs between judging a face and then responding to load (as opposed to the contrasting order seen in Experiments 1-3) may influence the efficacy of load, although this does not
contradict the general notion that perceptual load appears to have a role in impacting facial judgments for certain type of evaluations and valences.
4.2.3.4 Full model
Overall, reversing the order of responses so that the judgment responses came first did not have a significant impact on the pattern of modulation by perceptual load that we have observed in the last chapter.
A comparison of the results of experiments from the last Chapter and the reversed-order results just presented with a between experiment ANOVA revealed no main effect of experiment, for any of three groups; that is for trustworthiness F(1, 26) =1.18, MSE = .047, p = .28, η2 = .044, for dominance
F(1, 27) < 1, MSE = .045, p = .62 and for threat F(1, 30) < 1 , MSE = .063, p = .99 , η2 < 0.001, all had
no significant differences between experimental manipulations.
Additionally, none of the two or three-way interactions between experiment, load and valence were significant, except predictably (if one scrutinizes the graphs for face judgment accuracies) for a corresponding interaction for both trustworthiness and dominance between experiment and valence.
The slightly different general patterns of response for valence in trustworthiness (Experiments 1 and 4) and dominance (Experiments 2 and 5) were evident in the interaction between both of those experiments and valence.
The valences accuracies were less for the more trustworthy faces in Experiment 1 than
Experiments 4. Specifically trustworthiness +2SD and +3SD valence were less in Experiment 1 (M = 75 % and M = 79 % respectively) than Experiment 4 (M = 84 % and M = 93 % respectively) - (F(1, 26) =5.40, MSE = .01, p = .028, η2 = .17 and (F(1, 26) =9.41, MSE = .015, p = .005, η2 = .27).
Likewise for dominance there was a slight difference of overall valence between the
experimental iterations, which follow up pairwise testing revealed was driven by -2 SD valence being less in Experiment 2 (M = 74% vs M= .85) than Experiment 5 (F(1, 26) =4.86, MSE = .017, p = .036, η2 = .15).
4.2.3.5 Discussion
The latter three experiments (Experiments 4-6),broadly replicates the pattern of results of perceptual load effects on facial social judgment found in Experiments 1-3, even though the order of responses was reversed so that the categorization response came after the search response. Reaction times were not analysed as they were contaminated by order effects as the load task was now
performed after the face judgment – although encouragingly in all three experiments (4-6) the reaction times were significantly faster under low as opposed to high load (with no interactions or effects of valence).
As to be expected in any experimental replication, there were some differences, e.g. in Experiment 5 the high threat face accuracies for maximum threat +3SD valence were solidly and
significantly reduced under high load (low load M = 85 % vs. high load M= 66 %)), as opposed to a weaker impact (but still the largest of all the valences in that experiment) in Experiment 3 (low load M = 77 % vs. high load M= 69.5 %)).
The largest disparities amongst the experimental iterations were the differences for trustworthiness evaluations in Experiment 1 and 4, where the pattern of valence accuracies were altered, being less for the more trustworthy faces in Experiment 1 than Experiments 4. Specifically trustworthiness +2SD and +3SD valence were less in Experiment 1 (M = 75 % and M = 79 % respectively) than Experiment 4 (M = 84 % and M = 93% respectively). Encouragingly, however, in both instances, the effect of load was driven by trustworthy faces (although this was borne by +2SD valence faces being lower under high load in Experiment 4, rather than +3SD valence faces as in Experiment 1) and a comparison of the results of the experiments here and from the last Chapter revealed no main effect of experiment (for any of three groups).
It is worth mentioning briefly the role of any two target cost in processing that may occur. There is some evidence to suggest that split attention leads to reduced performance when targets appear in a display simultaneously and require independent identification and a separate response (Duncan, 1980), as in the experiments reported in this thesis (where the participants are performing both a search task and a facial judgment task, based on a single stimulus presentation). Since however, we are primarily interested in the relative difference between low and high load, the potential effects of any two target response do not impact our conclusions as it is the application of load which is critical for our inferences.
Furthermore, the high overall accuracies as observed in the experiments thus far, indicate that the consequences of any possible two-target cost if indeed present, are not substantive.
Where it is possible that any putative two target cost may be relevant, is with regards to the order of task e.g. whether the facial judgment or search task is performed first.
By and large, the similar pattern of results with both key press orders (the effects of load are present irrespective of the order of stimuli response (i.e. search and facial social judgments being reversed) in Experiments 1-3, and Experiments 4-6 do not appear to support this possibility. Although, perhaps some of the slight differences in the trustworthy results of Experiments 1 and 4 for example, may by as a result of slightly different consequences of split attention. Of course this is speculative, as it is possible that there may be slight memory cost instead. Indeed, the nature of a two target cost for experiments such as in this thesis, is itself debated, with some authors suggesting that in fact in dual type tasks, attending to the first stimulus may increase or boost performance in the second task – an attentional boost effect (Swallow & Jiang, 2010). The idea being that the target detection opens an attentional gate that briefly enhances the perceptual processing of coinciding information (Swallow & Jiang, 2014). Although, as I said earlier within this section, this does not impact our conclusions, or the assumption that perceptual processes are limited.
Perceptual load is the working hypothesis that we are employing, accounting for how attention influences which information is processed, where all available perceptual resources are used even if it results in poorer performance (Lavie, 1995). This assertion entails that increasing the perceptual load of the target implies a reduction in resources available for encoding the concurrent image. It is possible that the effect of image encoding may be somewhat offset by modest deviations or some form of interference due to alerting and arousal by the need to respond to two tasks (Posner & Boies, 1971). Reassuringly, however in the experiments is this section (Experiments 4-6) there were no main effects or interactions between valence and load (or indeed in Experiments 1-3) either for the search array results or reaction times (in Experiment 1-3) for the search task, suggesting that the load task was not subject to interference by the facial judgments tasks. Even so, it will be important for future research, given the conflicted findings in the face and attention literature, and the modest effects that we have demonstrated so far, to determine any possible effects of a dual-task interaction and whether this applies to tasks comprised of distinct processes such as semantic (character recognition) and facial judgment (face processing) as employed here.
Overall, reversing the order of responses so that the judgment responses came first did not have a significant impact on the pattern of modulation by perceptual load that we have observed in the last chapter. This suggests that the button order, if at all, only slightly impacted the participants' evaluations (arguably more so for trustworthiness judgments). This may indicate something specific about that trustworthy judgments, sampling variability or some subtle participant bias preferences, an issue we will return to and focus on in Experiment 10.
Taken as a whole, these results and the fact that in these experiments, participants did not have to pause their judgment response until after they had made the search response, weakens alternative accounts of the results being in terms of a perceptual load effect on working memory say, rather than on perceptual categorization sensitivity. This result provides some evidence to counter the criticism that it is not the perceptual aspects of the facial stimuli which are affected by increasing load but rather the fact that participants have to hold in memory their response which is then what is actually affected by perceptual load.
This adds further support to the hypothesis that the level of perceptual load in a task has a role in influencing facial social judgment perception.