The Value of Dimensional Models of Early Experience: Thinking Clearly About Concepts and Categories

Abstract

We review the three prevailing approaches-specificity, cumulative risk, and dimensional models-to conceptualizing the developmental consequences of early-life adversity and address fundamental problems with the characterization of these frameworks in a recent Perspectives on Psychological Science piece by Smith and Pollak. We respond to concerns raised by Smith and Pollak about dimensional models of early experience and highlight the value of these models for studying the developmental consequences of early-life adversity. Basic dimensions of adversity proposed in existing models include threat/harshness, deprivation, and unpredictability. These models identify core dimensions of early experience that cut across the categorical exposures that have been the focus of specificity and cumulative risk approaches (e.g., abuse, institutional rearing, chronic poverty); delineate aspects of early experience that are likely to influence brain and behavioral development; afford hypotheses about adaptive and maladaptive responses to different dimensions of adversity; and articulate specific mechanisms through which these dimensions exert their influences, conceptualizing experience-driven plasticity within an evolutionary-developmental framework. In doing so, dimensional models advance specific falsifiable hypotheses, grounded in neurodevelopmental and evolutionary principles, that are supported by accumulating evidence and provide fertile ground for empirical studies on early-life adversity.

Keywords: adversity; deprivation; early-life stress; experience-driven plasticity; harshness; threat; unpredictability.

Figure 1.. Approaches for conceptualizing childhood adversity.

Three distinct approaches have been used for assessing exposure to adversity in childhood and studying the mechanisms through which these experiences influence developmental outcomes. Adversity experiences are depicted in colored circles, developmental mechanisms (i.e., cognitive, emotional, social, and neurobiological processes influenced by adversity) are depicted with a gear symbol, and Δ symbolizes change. Outcomes (e.g., depression, anxiety, poor school performance) are depicted in black circles, though we acknowledge that the associations between different forms of adversity and specific outcomes may vary. The specificity approach involves measuring adversity experiences individually (i.e., one at a time), and assumes that developmental mechanisms influenced by different forms of adversity are largely distinct. Cumulative-risk involves counting the number of discrete adversity exposures and experiences, assuming that the effects of distinct adversities on developmental outcomes are equal and additive. Mechanisms through which these adversities influence development are often not specified and implicitly assumed to be general (i.e., shared across adversity types). Dimensional models were developed to address the limitations of specificity and cumulative-risk approaches. These models identify core dimensions of experience that occur in multiple types of adversity that can be assessed continuously as a function of the severity or chronicity of adversity experiences. Dimensional models specify the developmental mechanisms most likely to be influenced by these aspects of experience, including some that are shared across multiple dimensions (e.g., changes in the functioning of stress response systems) and others that are unique to certain dimensions. Experiences of deprivation are posited to relate most strongly to changes in cognitive development, whereas experiences of threat/harshness are most strongly related to changes in emotion processing and faster life history strategies, including earlier pubertal maturation and risky sexual behavior. Unpredictability is related to cognitive schemas that prioritize short-term versus long-term rewards, executive function components involved in monitoring changing environments (e.g., attention shifting), and faster life history strategies.