A parametric study of fear generalization to faces and non-face objects: relationship to discrimination thresholds

Abstract

Fear generalization is the production of fear responses to a stimulus that is similar—but not identical—to a threatening stimulus. Although prior studies have found that fear generalization magnitudes are qualitatively related to the degree of perceptual similarity to the threatening stimulus, the precise relationship between these two functions has not been measured systematically. Also, it remains unknown whether fear generalization mechanisms differ for social and non-social information. To examine these questions, we measured perceptual discrimination and fear generalization in the same subjects, using images of human faces and non-face control stimuli (“blobs”) that were perceptually matched to the faces. First, each subject’s ability to discriminate between pairs of faces or blobs was measured. Each subject then underwent a Pavlovian fear conditioning procedure, in which each of the paired conditioned stimuli (CS) were either followed (CS+) or not followed (CS−) by a shock. Skin conductance responses (SCRs) were also measured. Subjects were then presented with the CS+, CS− and five levels of a CS+-to-CS− morph continuum between the paired stimuli, which were identified based on individual discrimination thresholds. Finally, subjects rated the likelihood that each stimulus had been followed by a shock. Subjects showed both autonomic (SCR-based) and conscious (ratings-based) fear responses to morphs that they could not discriminate from the CS+ (generalization). For both faces and non-face objects, fear generalization was not found above discrimination thresholds. However, subjects exhibited greater fear generalization in the shock likelihood ratings compared to the SCRs, particularly for faces. These findings reveal that autonomic threat detection mechanisms in humans are highly sensitive to small perceptual differences between stimuli. Also, the conscious evaluation of threat shows broader generalization than autonomic responses, biased towards labeling a stimulus as threatening.

To perceive or not to perceive? Individual differences in perception predict rule induction and response generalization

“…For instance, the observation that the type of learning (simple vs. differential) influenced patterns of generalized responses and but not perception (Lovibond et al, 2020), suggests that both are not driven by the same process. Furthermore, a close relationship between perception and generalized responding has now been found in studies that assessed perception and generalized responding on the same trial (Struyf et al, 2017; or as in the current study in separate blocks (Holt et al, 2014;Lovibond et al, 2020;Tuominen et al, 2019), suggesting that their relationship also does not merely emerges due to the temporal relationship in their assessment.…”

Implicit and explicit systems differently predict possible dangers

“…Several lines of evidence have shown that dissociable neural systems encode the implicit and explicit memories of a threatening experience 11,12 . Dissociations between implicit and explicit learning in threat conditioning have been found in brain-damaged patients 36 , in studies reporting implicit fear learning in the absence of explicit contingency awareness 37–40 , during implicit fear discrimination for consciously indiscriminable stimuli 41,42 and in fear reduction through a procedure that eludes conscious exposure to the learned threat 43,44 . In humans, nonhuman primates and rats, many brain regions have been identified as involved in implicit fear generalization and discrimination processes 1,45 , such as the prefrontal and auditory cortices 46–50 , the amygdala 51,52 , and the insular cortex 5,53 .…”

Modeling Trait Anxiety: From Computational Processes to Personality

“…Finally, although generalization of aversive associations has usually been investigated using fear conditioning paradigms, generalization could sometimes be more evident at the level of conscious reports than at the autonomic level (154), perhaps reflecting different neural substrates [i.e., hippocampal rather than amygdalar; see Ref. (155)] and consistent with cognitive “expectancy models” of fear acquisition (156, 157).…”