Dyslexia is a neurodevelopmental disorder manifested in deficits in reading and spelling skills that is consistently associated with difficulties in phonological processing. Dyslexia is genetically transmitted, but its manifestation in a particular individual is thought to depend on the interaction of epigenetic and environmental factors. We adopt a novel interactional perspective on early linguistic environment and dyslexia by simultaneously studying two pre-existing factors, one maternal and one infant, that may contribute to these interactions; and two behaviours, one maternal and one infant, to index the effect of these factors. The maternal factor is whether mothers are themselves dyslexic or not (with/without dyslexia) and the infant factor is whether infants are at-/not-at family risk for dyslexia (due to their mother or father being dyslexic). The maternal behaviour is mothers' infant-directed speech (IDS), which typically involves vowel hyperarticulation, thought to benefit speech perception and language acquisition. The infant behaviour is auditory perception measured by infant sensitivity to amplitude envelope rise time, which has been found to be reduced in dyslexic children. Here, at-risk infants showed significantly poorer acoustic sensitivity than not-at-risk infants and mothers only hyperarticulated vowels to infants who were not at-risk for dyslexia. Mothers' own dyslexia status had no effect on IDS quality. Parental speech input is thus affected by infant risk status, with likely consequences for later linguistic development.