Aging is associated with worse emotion recognition (ER) relative to young adults1,2, and worse theory of mind (ToM)3. Collectively, we will refer to these abilities as social cognition. There have been different explanations given as to why older adults struggle on such tasks: they have a positivity bias that makes it difficult to process negative emotions, they have difficulty with still photos because these stimuli lack ecological validity, their difficulty stems from a failure to look at the eyes, their general cognitive decline makes it hard to identify emotions and mental states, their brain decline in frontal and temporal areas results in a decline in social cognition. These views have previously been critiqued4. For instance, older adults struggle with negative and positive emotions, they have difficulty with video stimuli not just still photos, and they have difficulty with emotion bodies and voices when a failure to look at the eyes isn’t relevant. Thus, these explanations do not seem adequate, yet general cognitive decline and brain decline are known features of aging and cannot be ruled out so easily. Therefore, we consider the evidence for general cognitive decline below, and we return to the brain decline explanation in the Discussion.
Does General Cognitive Decline Explain Worse Emotion Recognition in Older Adults?
Aging is accompanied by decline in core cognitive abilities such as processing speed, working memory, and fluid intelligence. Fluid intelligence refers to the ability to solve novel reasoning problems with minimal input from prior learning such as formal schooling. Fluid intelligence benefits from a faster processing speed and better working memory5,6, with processing speed, working memory and fluid intelligence all declining in old age7,8. Given these age-related declines in cognition, researchers have speculated that general cognitive decline might underlie older adults’ worse social cognition. Indeed, there have now been several studies that have examined this question that we review below, beginning with ER in young and middle-aged adults.
Young and middle-aged adults.
In order to examine the role of general cognition in older adults, we first consider the role of general cognition for ER in young and middle-aged adults. A number of studies indicate that the fluid and general intelligence of young and middle-aged adults is related to their ER. For instance, ER in young adults correlates with general measures of cognition tapping memory and fluid intelligence9. Likewise, in a study of young and middle-aged adults, ER was related to general intelligence (verbal ability, induction, sequential reasoning, quantitative reasoning)10.
These relations have been investigated more thoroughly in a recent meta-analysis11. Amongst young and middle-aged participants, finding there was a mean effect size of r = .19 between higher intelligence and better ER with similar effects on ER for crystallized IQ, fluid IQ, spatial ability, memory, and speed. They also directly compared those under 35 to those over 35 and found higher overall correlations in the older group (e.g., crystallized IQ: r<35 = .20, r>35 = .28; fluid IQ: r<35 = .18, r>35 = .25). Although crystallized IQ (e.g., vocabulary) correlated with ER, crystallized IQ generally maintains or improves with age12. Thus, it does not seem plausible that crystallized IQ underlies the age-related decrement in ER in older adults. Instead, given (a) the relation between general cognition and ER in young adults, and (b) the decline in general cognition in older adults, it seems plausible that (c) general cognitive decline might account for worse ER in older adults. Below, we consider relevant research.
Older adults.
There are a number of studies that have obtained correlations between general cognition and ER, either in a sample of older adults, or over a group of young and older adults13-22. There are also some studies that have not obtained significant correlations23-25. The contradiction in findings is complicated further by the fact that there are differences in how researchers have examined correlations, sometimes grouping all participants regardless of age, and sometimes examining correlations just in older adults themselves. In the latter case, the correlations provide information about potential decline only within the older adult group itself, rather than across the entire age span. However, if one wants to know whether correlations explain differences between young and older adults’ social cognition, it would make more sense to compute correlations over all participants, not just older adults.
Furthermore, in order to understand the relation between general and social cognition, it is necessary to do more than examine correlations. A key question is whether age-related difficulties are maintained after controlling for social cognition. Once again, however, research addressing this question is inconsistent. For instance, some studies indicate that age differences exist even after controlling for general cognition14,17,21,24-27. Yet, there are other studies where (a) age effects are eliminated for at least some of the emotion tasks administered when controlling for general cognition16,20,28,29, (b) age differences do not exist at all after controlling for general cognition15,30, or (c) age effects are substantially reduced. For instance, in one study there were “strong reductions” in effect size13,18,31.
Further compounding the difficulty in interpreting previous findings, there are important differences in the way in which researchers have indexed general cognition by using tests of speed, working memory, or fluid intelligence, as well as the tasks used to measure each of these abilities. Whereas it might be more informative to include multiple tests tapping different aspects of general cognitive abilities, 9 of 14 studies that have examined whether age effects are independent of general cognition have included a single task to measure a single cognitive ability13,18-21,25,28,30. Likewise, 9 of 14 studies have included a single task to measure social cognition13,15,16,18,27-31. These studies do not provide a comprehensive test of the relation between general and social cognition. What is needed, and what we provide in the present study, is an analysis with multiple tests that get at different aspects of both general and social cognition.
Adding to the confusion, inconsistencies have arisen even when the same task has been used to index general cognition. For instance, consider the studies that have given just a matrices task as a measure of general cognition. After controlling for matrices performance, three studies found age differences in social cognition19,21,28, one didn’t15, two found age differences on some social tasks but not others20,28, and one found a substantially reduced difference13. Thus, even when (a) the same task – matrices – is used to index general cognition, (b) matrices is one of the primary ways of examining fluid intelligence32, and (c) fluid intelligence is one of the most consistent abilities to decline in old age7, results still seem inconsistent.
In sum, (a) general cognition and social cognition are multi-faceted but previous studies have usually used a single measure of each, and (b) when one such single measure (matrices) has been used, the link to social cognition is inconsistent. Therefore, a more conclusive test of the relation between general and social cognition requires the inclusion of multiple tasks to measure different cognitive abilities.
A similar argument applies to tasks examining ER because different tasks present different information processing demands. For instance, some have claimed that dynamic stimuli (e.g., videos) should offer older adults a more ecologically valid stimulus33, which should ease difficulty. Yet, others have found that, in general, dynamic stimuli place a heavier demand on information processing resources than static stimuli34. That is, a dynamic emotional stimulus places a heavier demand on processing speed, working memory and fluid intelligence compared to still photos, because of the need for quick processing and updating of information as the display changes from one expression to another. Consistent with this argument, dynamic stimuli are generally more difficult34, and a meta-analysis of emotion tasks indicates the same; older adults have more consistent difficulties across emotions when given emotion videos than when given emotion photos1.
For these reasons, in our study we used three tasks each to measure different aspects of both general and social cognition (for a total of six tasks). No study has provided such an extensive battery of tasks (with five studies using a total of two tasks, seven studies using a total of three tasks, and two using four).
Does General Cognitive Decline Explain Worse Theory of Mind in Older Adults?
The previous section considered ER but a similar conflict in findings has arisen when researchers have examined the role of general cognition in older adults’ ToM. For instance, an early study examined the relation between processing speed, executive functioning (the Wisconsin Card Sorting Task) and ToM in young and older adults35. The ToM task (Strange Stories) required participants to explain unusual behaviour, and both processing speed and executive functioning correlated with ToM, although older adults were still worse than young adults after accounting for general cognition. Subsequently, a review of this study and many others concluded that, “ToM may be observed to function independently from general cognition in aging, but further investigation is needed to confirm this point” (p.32)36.
Since that time, subsequent studies have produced conflicting findings. For instance, one study gave participants aged 17 to 95 the Strange Stories task, along with a Stroop task, a working memory task, and an empathy scale37. Performance on the cognitive measures as well as empathy correlated with performance on the ToM task, and when entered into a regression, explained all of the variance in ToM performance, with age not explaining significant variance.
Another study varied the executive function (EF) demands of a ToM task and found that the task with high EF demands led to age differences, whereas the task with low EF demands produced no age differences38. However, they measured ToM with 20 false and 20 true belief tasks, and this is a likely shortcoming of this study in that these tasks are passed by 4- to 5-year-old children typically, and therefore, do not provide a sensitive measure of ToM. It is probable that failure occurs only because of waning attention over 40 trials rather than a lack of conceptual insight, and this likely explains the relation to EF in this study, whereas a more conceptually demanding ToM task might be unrelated to EF.
Other researchers have examined EF abilities on tasks such as Trail Making (tapping speed and fluid IQ), Backwards Digit Span (working memory), the Tower of London (planning, inhibition), and matrices (fluid IQ) in a group of young adults39. None of these tasks correlated with performance on the Eyes task (judging complex emotions and mental states in the eyes). On the Strange stories task, only matrices correlated, but there was no older group to determine whether age differences still existed.
Still another study examined the Eyes task, along with aspects of executive function in a group of older adults40. Block Design and inhibitory ability correlated with ToM, but there was no younger group to determine whether there were age differences having accounted for general cognition.
In sum, research presents a rather confusing picture. Sometimes general cognition correlates with ToM and sometimes it doesn’t. If general cognition correlates, sometimes age differences persist when controlling for general cognition, and sometimes they don’t.
Present Study
Previous studies of the relation between general cognition and ER have usually used one task that measures a single cognitive ability, with studies having obtained inconsistent findings. Inconsistency is also the norm when one narrows the lens to look only at studies employing a single cognitive task such as matrices. Yet there are multiple cognitive skills that are relevant to social cognition, with different social cognition tasks having different cognitive demands. In an effort to provide a more comprehensive index of cognitive ability, we used three tasks, all of which measured a different cognitive skill, and with all skills thought to be central to cognitive decline: speed of processing, working memory, and fluid IQ6.
Further, in a deliberate effort to vary the cognitive demands of the tasks tapping social cognition, we also included three social tasks: the Eyes task, an Emotion Photos task, and an Emotion Morph task. The Eyes task is typically thought of as a ToM measure, although it has more recently been argued that it is better construed as a test of complex emotions41. Analysis of the 36 items indicates that 9 unambiguously measure emotion (e.g., despondent), 13 have an emotional valence (e.g., insisting), and 14 are more straightforward cognitive items (e.g., preoccupied). It might, therefore, represent something of a cross between a measure of more complex emotions and mental states, but can be construed as a more demanding task than classic ER tasks, which examine only basic emotions (anger, sadness, fear, disgust, surprise, and happiness). The Emotion Photos task is a standard ER task in which we presented still photos of the face expressing basic emotions. The Emotion Morph task presented dynamic stimuli, with emotion faces that gradually morphed from one basic emotion into a different basic emotion, and the participant’s task was to identify the new emotion as quickly as possible.
These three tasks tapping social cognition had intentionally differing characteristics that allowed us to carefully examine the relation between general cognition and social cognition. Again, the Eyes task required an understanding of complex emotions and mental states, but used still photos. The Emotion Photos tasks examined basic emotions and presented still photos. Neither of these tasks had a time limit on responding or required integration of information over time. In contrast, the Emotion Morph task required both of these things. As stated above, the Emotion Morph task should place a heavier demand on processing speed, working memory and fluid intelligence because of the need for quick processing and updating of information as the display changes from one thing to another34. This is particularly so because the task was speeded, in that participants were instructed to identify the new emotion as quickly as possible. Thus, to take into account both speed and accuracy, we computed a “balanced integration score” that gave equal emphasis to each. Given that speed was integral to optimal performance, and speed is a core cognitive ability that declines with age, logic would have it that the Emotion Morph task should be more heavily correlated with general cognition than the Eyes or Emotion Photos tasks.