Based on their New York Longitudinal Study, psychiatrists Alexander Thomas and Stella Chess proposed a classification of three primary infant temperaments. These categories—easy, difficult, and slow-to-warm-up—describe distinct patterns in how infants behave and react to new situations and stimuli.

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Temperament refers to innate, biologically-based traits that influence how an individual behaves and reacts. This biological basis is supported by the fact that temperament is observable very early in life. Key dimensions of temperament include reactivity and self-regulation.

Temperament in Personality

Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020, April 22). Psychology (2nd ed.). OpenStax. https://openstax.org/books/psychology-2e/pages/1-introduction

OpenStax Psychology (2nd ed.) Textbook

Thomas and Chess's Three Infant Temperaments

Research indicates that two fundamental dimensions of temperament—reactivity and self-regulation—are significant and enduring components of an individual's adult personality.

Temperament Dimensions in Adult Personality

Reactivity, a key dimension of temperament, describes how an individual responds to novel or challenging stimuli in their environment. For instance, some individuals may react with high anxiety to new situations, while others may show little to no reaction.

Reactivity in Temperament

Self-regulation, a key dimension of temperament, is the capacity to control one's response to new or challenging environmental stimuli. It involves an individual's ability to manage their initial reactions, which are governed by their level of reactivity.

Self-Regulation in Temperament

Personality theorists Hans and Sybil Eysenck developed a theory centered on temperament, which they defined as inborn, genetically based personality differences. Believing that personality is largely governed by biology, they identified two primary dimensions: extroversion versus introversion and neuroticism versus stability. Their model suggests that extroverts are sociable and outgoing, while introverts prefer solitude. Similarly, individuals high in neuroticism are anxious and have a reactive stress response, whereas those high in stability are more emotionally resilient. A third dimension, psychoticism versus superego control, was later added to their model.

Hans and Sybil Eysenck's Theory of Personality

Based on the provided scenario, explain how the concept of innate, biologically-based individual differences in behavior accounts for the consistent patterns observed in Leo and Mia. In your explanation, be sure to address the key characteristics that define this concept.

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