Negative emotions are typically high, and typically stay high over time, in caregivers of children with autism. The severity of autism-related symptoms on the other hand tends to improve over time, reducing as the child gets older. Why caregivers’ negative emotions continue to be high at a time when autism symptom severity is improving remains puzzling. This exploratory study asks whether prevalence-induced concept change (PICC) might provide one plausible explanation. A sample of N=34 participants, of which 17 were caregivers of children with autism and 17 were non-caregiving controls, completed questionnaires assessing negative emotions. PICC was assessed via an online paradigm; participants were shown a face on screen for 500ms and asked, following its disappearance, whether it conveyed a negative (i.e., sad) or a neutral expression. Neutral faces mistaken for sad faces, as our outcome variable of interest, were summed across trials. The prevalence of negative faces was gradually reduced across four experimental blocks (50 trials per block). Mixed ANOVA yielded a significant main effect of block. That is, neutral faces were more likely to be mistaken for sad faces as sad faces became less prevalent across blocks. This pattern of change varied by group; caregivers were more likely to mistake neutral faces for sad faces as sad faces reduced in prevalence across blocks. Errors made by the control group did not vary across blocks. Caregivers’ concept of ‘negative, therefore, seems sensitive to change, redefining its parameters as negative events become less prevalent. PICC might explain why caregivers’ negative emotions remain high when autism symptom severity, as one well-known predictor of those negative emotions, is reducing in prevalence. The implications of these findings for caregivers’ psychological well-being and, by association, care recipient quality of life are considered.