Sensitive periods are those time periods during which certain __________ are…

Concept: A foundational principle of developmental psychology is that some traits are not shaped by a constant, unchanging influence but by experiences that matter most during defined developmental time-windows. A ‘sensitive period’ is exactly such a window — input received during that specific phase has an outsized effect on how normal development unfolds, while the same input arriving outside that window has far less effect.

Application: The statement defines sensitive periods as time periods during which certain ___ are especially important for the course of normal development. This is precisely how environmental factors work in this framework — external experiences and stimuli whose developmental impact depends heavily on timing. So the blank is correctly completed by environmental factors.

Why the other options do not fit:

• genetic predispositions — inherited biological tendencies fixed at conception; their influence does not depend on a specific developmental time-window.

• ethnic factors — relate to a person’s cultural or community background, not to an influence whose importance is concentrated in a particular developmental window.

• hereditary factors — biologically inherited traits passed on from parents; like genetic predisposition, a stable characteristic rather than a time-window-dependent influence.

Cross-check: This matches classic illustrations of sensitive periods — such as early language acquisition or attachment formation — where the presence or timing of specific experiences during an early window critically shapes the developmental outcome, confirming environmental factors as the concept being described.