Inclusion Criteria:  circulatory and respiratory stability; readiness for oral feeding according to each child's Speech-Language Pathologist assessment; prematurely born infants who will be in the process of transfer from enteral nutrition to full oral feeding and will be fed orally at least 4 times within twenty-four hours; researcher must be a right handed person (right hand is the dominant hand); each infant will be fed with one kind of bottle and nipple; parents will give a informed consent to participate their infant in the study.  Exclusion Criteria:  disorders which could significantly affect the feeding course, such as cleft lip and/or palate, facial paralysis and/or congenital defects of the facial skeleton; the presence of detected congenital abnormalities and metabolic diseases; newborns after abdomen chirurgical treatment; low Apgar score (less than 5 points at the 5th and 10th minute of the measurement); administered analgesics, anticonvulsants and sedatives <72 hours from extubation prior the trial; parenterally fed infants; infants with administered intravenous infusion with glucose; parents refusal to participate in the study or when bottle-feeding will not be the parental preference.