Age Effect On Neural Temporal Dynamics Of Facial Emotion Processing And Its Modulation

Although the pathophysiology remains unclear,selective impairments in facial affect identification have been the assumption that the impairments may have a role in the etiopathogenesis of psychiatric and neurological disorders.Ageing may also be associated with changes in facial emotion identification.Numerous behavioural studies have identified age-related decline in labeling negative facial expressions and a preservation in labeling happy expressions.By tracking the time course of cognitive processing at an early stage of stimulus encoding and with resolution in the order of milliseconds,the event-related potential(ERP)may even have the potential to be excellent neural markers of the early involvement of perceptual face knowledge that could be useful in understanding human cognition development and pathology.The behavioural and ERP indices of facial emotion processing were analyzed in the present study.In the experiment 1,the facial emotion labeling task was adopted to investigate age-related changes by objective isolation and direct quantification of particular ERP components related to facial encoding and affect decoding processes to examined the influence of aging on the discrimination of facial expressions and its relationship with cognitive function.In the experiment 2,we manipulated perceptual load by varying the demand for letter tasks in which faces were presented centrally as distractors blended with task-relevant letter strings,while we measured the extent to which a distractor emotional face was processed under conditions of low(color discrimination task)or high(letter identification task)perceptual load by analyzing the emotion related ERP components.We also considered that the use of different visual windows to manipulate focus of attention(focused attention condition:letter strings were superimposed on the nose region of the distractor faces;less focused attention condition:increase the spatial scope of attention by presenting the circular array of letters around the edge of the distractor faces)which may potentially reveal a ubiquitous pattern of scanpath effects on facial emotion processing in older adults.This approach should help us achieve a broader understanding of how perceptual load and focus of attention might or might not be related to the emotional faces processing,and the extent to which modulating influences of perceptual load and focus of attention on early visual processing of emotional faces can occur in older adults.In the experiment 3,the present study to explore whether it is positivity effect or deficits in facial emotion processing in older adults from behavioural and ERP level.According to the positivity effect hypothesis,the present study explored the positivity effect from the "positivity enhancements","negativity reductions",and "rate neutral pictures as more positive" respectively.In the experiment 1,During early sensory processing of emotional faces,an insignificant group difference in P100 amplitudes suggests that early detection of facial emotions remains relatively intact in the older adults.During structural encoding of facial features,highly similar to behavioural results,N170 elicited by negative faces was enhanceed in older adults relative to their younger counterparts,while right hemispheric N170 elicited by positive faces was relatively intact.Moreover,VPP elicited by negative faces was attenuated in older adults relative to their younger counterparts.Higher N170 and VPP for negative faces were correlated with better performance for labeling negative faces.These findings suggest that there may be functional dissociations between N170 and VPP,VPP may be better positioned to reflect contributions from frontal sources,and potentially interrupted frontal-parietal interactions in older adults may contribute to deficit in facial emotion categorization.Moreover,impaired negative face identification(indicated by reduced accuracy and slower speeds)was associated with impairment in cognitive function(measured by MoCA and MMSE),suggesting that cognitive functions may play a role in explicit facial emotion perception,and contribute to problematic processing and identification of negative expressions in older adults.In the experiment 2,interference(indicated by accuracy rate and reaction time of central task)from task-irrelevant sad faces was insignificant in older adults comparing to those in young adults under focused attention condition.The ERP results showed that the P100 latency elicited by happy faces under high perceptual load with larger receptive field sizes was faster when comparing to young adults suggesting that older adults tended to process emotional faces holistically under less focused attention.In older adults,the N170 amplitudes were modulated by focus of attention(N170 elicited by sad and neutral faces were enhanced under focused attention condition),but not perceptual load.While,the N170 latency were modulated by affect effect(N170 elicited by sad faces were significantly delayed),but not sensitive to the modulation of scanpath effect and perceptual load.The P2 amplitudes were modulated by perceptual load and focus of attention.Under high perceptual load,P2 amplitudes elicited by sad faces under focused attention in older adults were smaller than those in young adults,while P2 amplitudes elicited by happy faces under focused attention in older adults were smaller than those in young adults,suggesting that valence-specific processing strategy may help to improve secondary structural encoding of negative facial expression.In the experiment 3,we analyzed errors types and its frequency for emotion labeling to examine whether there was a tendency to mislabeling negative or neutral faces as positive faces in older adults.A higher proportion of mislabeling neural faces as negative faces rather than mislabeling neural faces as positive faces was found in young adults.However,this effect has not been observed in older adults.Moreover,there were no significant group differences in error types for mislabeling negative faces or positive faces.We also re-calculated the ERP data using the method reported by Hilimire and colleagues,but no age-related stronger positive deflection for happy faces at frontal scalp sites over the time-window of P100 was observed.Neither enhanced N170 for positive faces,nor attenuated N170 for negative faces,has been observed.On the emotional faces recognition task,the hit rates(correctly identified learned faces)for emotional faces(sad and happy faces)were higher than those of neutral faces under low perceptual load,while the hit rates of sad faces were higher than those of happy faces under high perceptual load,suggesting that the emotional facial expressions captured attention and suppressed memory access for competing faces,but only negative facial expression enjoyed privileged memory access.The findings in the experiment 1 add to the knowledge base on age-associated changes on neural temporal dynamics for facial expression processing.Consistent with the behavioural differences,early visual processing of negative expressions may be more impaired than neutral and positive expressions because of insufficient configural encoding in older adults.In older adults,interrupted frontal-parietal interactions during structural encoding of negative faces may contribute to deficit in labeling negative facses.Cognitive functions may also play a role in problematic categorization of negative faces in older adults.The results in the experiment 2 support that the secondary structural encoding and late prossesing of emotional faces were modulated by perceptual load and focus of attention.However,early sensory processing and structural encoding of emotional faces were only modulated by focus of attention.In older adults,there was a tendency to processing emotional faces holistically.The focused attention at eye region may benefit structural encoding and perceptual encoding of emotional faces in older adults.In the experiment 3,we did not observe positivity bias or negativity avoidance during facial emotion perception,identification and recognition.In conclusion,the findings we observed in the present study suggest that,in older adults,reduced cognitive functions may play a role in problematic explicit identification of negative expressions,and changes in facial emotion identification are,to some extent,a vulnerability factor of aging.Valence-specific processing strategy may help to improve structural encoding and perceptual encoding of negative facial expression.