Sucking Behavior

Abstract

Sucking behavior is a type of behavior in which an infant draws fluid or applies rhythmic negative pressure with the mouth, present from before birth and organized into a patterned motor rhythm. Psychologists distinguish nutritive sucking, which delivers milk, from non-nutritive sucking on a pacifier or finger, which delivers none; the two differ systematically in rate and temporal structure. Beyond feeding, sucking became a productive tool in developmental science: an infant will change how fast or hard it sucks to obtain a sound, voice, or flavor, turning the mouth into a readout of what it can perceive and remember. This article reviews how sucking is defined and measured, how the high-amplitude sucking paradigm revealed infant speech perception and memory, how it carries flavor learning, and how non-nutritive sucking supports preterm nutrition, pain relief, and lower sudden-death risk.

Keywords: sucking behavior, non-nutritive sucking, high-amplitude sucking, infant perception, flavor learning

Sucking is among the earliest coordinated behaviors a human performs, and Wolff showed that it is not a formless reflex but a serially organized rhythm of bursts and pauses whose structure is stable enough to measure (Wolff, 1968). Because the infant controls that rhythm, it can be made contingent on a stimulus, and Siqueland and DeLucia demonstrated that newborns will modulate non-nutritive sucking simply to turn on a visual display, establishing sucking as an operant response (Siqueland & DeLucia, 1969). That single methodological fact, that an infant will work with its mouth to produce an interesting consequence, underlies much of what is known about the infant mind.

What Sucking Behavior Is

Sucking behavior is the rhythmic application of the lips, tongue, and jaw to draw fluid or to generate suction without intake. It begins in utero and is functional at birth, where it must coordinate with swallowing and breathing for the infant to feed. Rather than a single reflex, mature sucking is a serially organized pattern: the infant produces a burst of sucks at a fairly regular rate, pauses, and then resumes, and the length and spacing of these bursts and pauses form a measurable temporal signature (Wolff, 1968).

Two broad modes are distinguished by consequence. Nutritive sucking occurs during feeding and delivers milk; it tends to be slower and more continuous, paced by the need to swallow. Non-nutritive sucking occurs on a pacifier, finger, or empty nipple and delivers no fluid; it is faster and shows the clearer burst-pause structure. The mechanics within a suck can themselves be separated: Sameroff distinguished the expression component, in which the tongue and jaw compress the nipple, from the suction component, in which negative pressure is generated in the mouth, and showed that newborns adjust these components to the feeding situation (Sameroff, 1968). The demonstration below contrasts the temporal pattern of nutritive and non-nutritive sucking.

Nutritive vs. non-nutritive sucking rhythm

Each upward spike is one suck across a 10-second window. Switch between the two modes to compare their temporal structure: nutritive sucking is slower and evenly spaced, while non-nutritive sucking is faster and organized into bursts separated by pauses.

Nutritive (~1 suck/s, continuous): Nutritive sucking delivers milk and is slower and more continuous, paced by the need to swallow. This mode shows 10 sucks in the window.

Table 1 summarizes how the two modes differ on the dimensions that matter for measurement and for clinical judgment. The modes are endpoints of a continuum rather than rigid categories, and a single feeding session can move between them.

Sucking as a Window Into the Infant Mind

Because non-nutritive sucking is an operant response the infant controls, it can be made to depend on a stimulus, and the infant's willingness to work for that stimulus reveals what it perceives. Siqueland and DeLucia first exploited this by reinforcing sucking with a visual display, showing that newborns suck more to keep an interesting sight available (Siqueland & DeLucia, 1969). The method was then refined into the high-amplitude sucking paradigm, in which only sucks above an amplitude criterion trigger a sound; the infant first sucks vigorously as the sound plays, then habituates as the sound becomes familiar and sucking falls, and finally, if a new sound is introduced, dishabituates—sucking hard again if and only if it detects the change.

Eimas and colleagues used exactly this logic to make a landmark discovery: one- and four-month-old infants recovered their sucking to an acoustic change that crossed the adult boundary between /ba/ and /pa/ but not to an equally large change within a single category, showing that infants perceive speech categorically long before they talk (Eimas, Siqueland, Jusczyk, & Vigorito, 1971). DeCasper and Fifer turned the same contingent-sucking method toward memory, arranging for newborns to produce their own mother's voice by sucking at one rate and a stranger's by sucking at another; infants adjusted their sucking to hear the maternal voice, implying they recognized a voice heard before birth (DeCasper & Fifer, 1980). Later work extended the approach to the building blocks of language, with Jusczyk and Aslin showing that infants detect familiar sound patterns of words embedded in fluent speech (Jusczyk & Aslin, 1995). The demonstration below illustrates the habituation and recovery that make the paradigm work.

The high-amplitude sucking paradigm

Step through the four phases. Choose whether the test sound differs across a phonetic category boundary or within a single category. Only an across-category change produces strong dishabituation, the recovery of sucking that reveals the infant perceives speech categorically.

Sucking is recorded before any sound is contingent on it.

Flavor, Feeding, and Development

Sucking is also the channel through which early flavor experience reaches the infant. Mennella and colleagues showed that flavors from the maternal diet pass into amniotic fluid and milk and that infants later suck differently in response to those familiar flavors, evidence that flavor learning begins before weaning and is expressed in feeding behavior (Mennella, Jagnow, & Beauchamp, 2001). The maturation of sucking itself is a developmental milestone: coordinating sucking with swallowing and breathing is one of the last competencies a preterm infant acquires before oral feeding is safe, and Zhao and colleagues systematically reviewed the maternal, infant, and care factors that advance or delay that competence (Zhao et al., 2024). How the infant actually extracts milk has itself been reconsidered: Douglas and Geddes argued from ultrasound studies for a gestalt model of the suck in which tongue movement and intraoral vacuum, rather than a simple stripping action, drive milk transfer, with direct implications for how feeding difficulties are assessed and supported (Douglas & Geddes, 2018).

Clinical and Applied Significance

The same non-nutritive sucking that serves research has direct clinical uses. In preterm infants, offering a pacifier during tube feeding, a practice called non-nutritive sucking, is associated with a faster transition to oral feeding and shorter hospital stay, and Foster and colleagues synthesized the controlled trials supporting it (Foster, Psaila, & Patterson, 2016). Sucking is also one of the most effective non-pharmacological ways to relieve procedural pain in neonates: Stevens and colleagues found in a large systematic review that oral sucrose, which is typically delivered on a pacifier and so combines a sweet taste with non-nutritive sucking, reduces pain responses to heel lances and injections (Stevens, Yamada, Ohlsson, Haliburton, & Shorkey, 2016). Finally, pacifier use at sleep is associated with a lower risk of sudden infant death syndrome; Hauck and colleagues quantified this protective association in a meta-analysis, making non-nutritive sucking a component of safe-sleep guidance (Hauck, Omojokun, & Siadaty, 2005). The demonstration below illustrates how sucking-based interventions combine to lower an infant's pain response.

Additive model of sucking-based pain relief

An infant undergoing a heel lance has a baseline pain score of 7.0 on a 0-to-10 scale. Toggle the two interventions. Non-nutritive sucking subtracts 1.5 points and oral sucrose subtracts 2.5; because sucrose is delivered on a pacifier, the two combine additively, and the predicted score is held at a floor of 0.

Predicted score: 7.0, a reduction of 0.0 points (0%) from baseline. Selecting both interventions subtracts 4.0 points, cutting the expected response from 7.0 to 3.0, which is why sweet taste and sucking are recommended together.

Worked Example

Consider an infant undergoing a heel lance, with pain scored on an illustrative 0 to 10 scale where higher means more distress. With no intervention the expected score is 7.0. Suppose, as an additive approximation of the trial literature, that offering a pacifier for non-nutritive sucking lowers the score by 1.5 points and that 24 percent oral sucrose lowers it by 2.5 points. Used alone, non-nutritive sucking gives 7.0 - 1.5 = 5.5 and sucrose gives 7.0 - 2.5 = 4.5. Because sucrose is normally delivered on a pacifier, the two act together, and under the additive model their combined effect is 1.5 + 2.5 = 4.0 points, for a predicted score of 7.0 - 4.0 = 3.0. The combination therefore cuts the expected pain response from 7.0 to 3.0, a reduction of roughly 57 percent, which is why sweet taste plus sucking is recommended together rather than either alone. The demonstration above uses exactly this additive model, so selecting both interventions subtracts 4.0 points and the predicted score floor is clamped at 0.

Key Researchers

Anthony J. DeCasper

(1940-2016). Psychologist at the University of North Carolina at Greensboro; using a contingent-sucking method he showed that newborns prefer and will work to hear the maternal voice, establishing prenatal auditory memory. In memoriam

Peter D. Eimas

(1934-2005). Cognitive scientist at Brown University; he used the high-amplitude sucking paradigm to demonstrate categorical speech perception in one-month-old infants. Wikipedia

Donna T. Geddes

(living). Professor of Human Lactation at the University of Western Australia; her ultrasound studies of infant suck mechanics support a gestalt model of milk transfer. ORCID

Julie A. Mennella

(living). Biopsychologist at the Monell Chemical Senses Center; she demonstrated prenatal and postnatal flavor learning and its expression in infant sucking. ORCID

Bonnie Stevens

(living). Nurse scientist at the University of Toronto and The Hospital for Sick Children; she established the evidence base for sucrose and non-nutritive sucking in relieving neonatal procedural pain. ORCID

Discussion

Sucking occupies an unusual place in psychology because it is at once a vital behavior in its own right and a uniquely convenient instrument for studying others. As a behavior, it is the infant's first coordinated motor achievement, organized from birth into a measurable rhythm and tied to the life-sustaining acts of feeding and breathing (Wolff, 1968; Sameroff, 1968). As an instrument, its operant controllability let researchers ask a preverbal infant what it can hear, discriminate, and remember, yielding the foundational findings that infants perceive speech categorically and recognize the maternal voice heard in the womb (Eimas, Siqueland, Jusczyk, & Vigorito, 1971; DeCasper & Fifer, 1980).

The two faces of sucking meet in clinical practice, where understanding the behavior guides care of the most fragile infants. Non-nutritive sucking advances feeding competence, relieves pain, and reduces sudden-death risk, and these applications draw on the same facts about rate, structure, and reinforcement that make sucking a research tool (Foster, Psaila, & Patterson, 2016; Stevens, Yamada, Ohlsson, Haliburton, & Shorkey, 2016; Hauck, Omojokun, & Siadaty, 2005). The through-line is that sucking is never merely reflexive consumption; it is a sensitive, controllable behavior whose patterning carries information about perception, memory, flavor, and well-being.

Current Directions

The methodological front remains active. Sjuls reviewed the high-amplitude sucking procedure itself, cataloguing the many variants in criterion-setting, habituation rules, and analysis that have accumulated over five decades and calling for standardization so that infant findings can be compared across laboratories (Sjuls, 2025). On the developmental side, attention has shifted to the preterm population, where the maturation of safe oral feeding is both a clinical bottleneck and a theoretical puzzle about motor coordination, and Zhao and colleagues mapped the modifiable factors that shape it (Zhao et al., 2024). Reassessments of suck mechanics from imaging continue to revise how feeding difficulties are understood and supported (Douglas & Geddes, 2018). Open questions concern how far the classic contingent-sucking findings replicate under standardized procedures, and how the physiology of the suck maps onto the behavioral measures that psychology has long relied on.

Common Misconceptions

Sucking is a simple reflex with no structure.

It is a serially organized rhythm of bursts and pauses that the infant modulates, not a formless or purely automatic response (Wolff, 1968).

Non-nutritive sucking is just self-soothing with no use.

It is an operant response that supports preterm feeding, relieves procedural pain, and is used experimentally to measure infant perception (Foster, Psaila, & Patterson, 2016).

Newborns cannot discriminate speech sounds.

High-amplitude sucking showed that one-month-olds discriminate speech categorically, well before they produce language (Eimas, Siqueland, Jusczyk, & Vigorito, 1971).

Glossary

Burst-pause pattern.

The temporal organization of sucking into runs of sucks separated by pauses, a measurable signature of the behavior.

Categorical perception.

Perceiving a continuous acoustic change as a sudden shift between discrete categories, shown for speech in infants via sucking.

Contingent sucking.

An arrangement in which a stimulus is delivered only when the infant sucks, making sucking an operant that reveals preference.

Dishabituation.

The recovery of a declined response when a novel stimulus is introduced, used to infer that the infant detects the change.

Expression component.

The part of a suck in which the tongue and jaw compress the nipple, distinguished from the suction component.

Flavor learning.

The acquisition of preferences for flavors experienced through amniotic fluid and milk, expressed later in sucking.

Habituation.

The gradual decline of a response to a repeated or unchanging stimulus, seen as falling sucking rate in the paradigm.

High-amplitude sucking paradigm.

A method in which only vigorous sucks trigger a sound, so habituation and recovery index what an infant perceives.

Non-nutritive sucking.

Sucking on a pacifier, finger, or empty nipple that delivers no fluid, faster and more clearly patterned into bursts.

Nutritive sucking.

Sucking during feeding that delivers milk, typically slower and more continuous than non-nutritive sucking.

Operant response.

A behavior whose rate is controlled by its consequences; sucking is one, which is what lets it index infant preference.

Procedural pain.

Pain from medical procedures such as a heel lance, reduced in neonates by sucrose combined with non-nutritive sucking.

Suck-swallow-breathe coordination.

The timed integration of sucking, swallowing, and breathing required for safe oral feeding, a late preterm milestone.

Suction component.

The part of a suck in which negative intraoral pressure draws fluid, distinguished from the expression component.

Sudden infant death syndrome.

The sudden unexplained death of an infant during sleep, whose risk is lowered by pacifier use at sleep.

Frequently Asked Questions

What is sucking behavior?

It is the rhythmic application of the lips, tongue, and jaw to draw fluid or generate suction, present from before birth and organized into measurable bursts and pauses (Wolff, 1968).

What is the difference between nutritive and non-nutritive sucking?

Nutritive sucking occurs during feeding and delivers milk, tending to be slower and more continuous, whereas non-nutritive sucking on a pacifier or finger delivers no fluid and is faster with clearer bursts (Sameroff, 1968).

Why is sucking used to study infant perception?

Because non-nutritive sucking is an operant response the infant controls, researchers can make a sound or image depend on it and read off what the infant perceives from how it sucks (Siqueland & DeLucia, 1969).

What did the high-amplitude sucking paradigm reveal about speech?

It showed that one- and four-month-old infants discriminate speech sounds categorically, recovering their sucking to a change across a phonetic boundary but not to an equal change within a category (Eimas, Siqueland, Jusczyk, & Vigorito, 1971).

Can newborns recognize their mother's voice?

Yes; newborns adjusted their sucking to produce the maternal voice over a stranger's, implying they recognized a voice heard before birth (DeCasper & Fifer, 1980).

Does non-nutritive sucking help preterm infants?

Offering a pacifier during tube feeding is associated with a faster transition to oral feeding and shorter hospital stay in preterm infants (Foster, Psaila, & Patterson, 2016).

How does sucking relieve pain in babies?

Sweet taste delivered on a pacifier combines sucrose with non-nutritive sucking and reduces pain responses to procedures such as heel lances and injections (Stevens, Yamada, Ohlsson, Haliburton, & Shorkey, 2016).

Do pacifiers affect the risk of sudden infant death?

Pacifier use at sleep is associated with a lower risk of sudden infant death syndrome and is included in safe-sleep guidance (Hauck, Omojokun, & Siadaty, 2005).

References