When do vowel sounds sound similar to each other?

Vowel sounds can sound similar to each other particularly when they are weakly stressed. In linguistic terms, weak stress often involves a reduction of the vowel sound, leading it to become more centralized or less distinct. This phenomenon is especially common in unstressed syllables, where vowels tend to lose their full quality and may resemble one another. For example, the vowel in a weakly stressed syllable may sound more like a schwa or another centralized vowel, which contributes to the similarity between sounds.

While it is true that factors like loudness, speed, and accent can influence vowel pronunciation, weak stress plays a direct role in causing vowels to lose their distinctive qualities, thereby making them sound more alike. This is a crucial aspect of phonetics and phonology that highlights how stress patterns impact the way vowels are articulated in speech.