Immediately after birth, infants of most species rely largely on parental care-taking behavior, such as protecting and feeding. Care-taking behavior is crucial for the survival of the next generation and thus secures the survival of the whole species. Characteristics inherent in infant faces facilitate such behavior. For example, Konrad Lorenz (1943) 
described the Kindchenschema
as an innate releasing mechanism for care-taking behavior. According to Lorenz, the Kindchenschema works as a trigger for instinctive behavior such as taking a child into one’s arms. The Kindchenschema is characterized by pedomorphic features such as a relatively large head compared to the size of the body, a relatively big cranium compared to the facial bones, large eyes that lie below the horizontal midline of the skull, a soft-elastic surface texture, and round and protruding cheeks. Infants that conform to the Kindchenschema are commonly described as cute and evoke positive affective approach behavior.
Several investigations found empirical support for Lorenz’ observations 
. Sternglanz and colleagues (1977) 
parametrically varied eye height, eye width, iris size, and vertical feature position and had participants rate the attractiveness of these faces. They found that especially a large forehead associated with a small chin and large eyes make a baby face look cute. Glocker and colleagues (2009) 
varied the width and the length of the whole face and the size of the forehead, the eyes, the nose, and the mouth of infant faces. A round face, a high forehead, big eyes, a small nose, and a small mouth were defined as “high” Kindchenschema features. They found that cuteness ratings were positively related to the extent of the Kindchenschema. Furthermore, the level of Kindchenschema correlates with positive attributions such as cuteness, warmth, and honesty 
, and has a positive emotional influence on mother-child interaction. Mothers of cute babies show more affectionate interactions compared to mothers with relatively less cute babies 
Lorenz (1943) 
claimed that the Kindchenschema is found in various species (e.g., humans, ducks, hares, tigers, lions, and dogs). To date, there is only one recent study that experimentally scrutinized the universality of the Kinschenschema. Little (2012) 
systematically varied the proportion of adult- and babyfacedness in cats, human babies, and adults by approximating their shape to human adult and baby composite faces. The results of a cuteness-rating task revealed that both cat and human faces were assessed cuter when approximated towards the shape of a human baby face compared to when approximated towards the shape of a human adult face. Thus, facial shape adopted from human infants (small jaw, large forehead) influenced the cuteness evaluation of cat faces. Our study went beyond the influence of facial shape on cuteness perception. We used a perceptual adaptation paradigm to test whether the processing of cuteness is species-specific or whether a generic mechanism underlies the perception of cuteness.
Perceptual adaptation is characterized by a change in the perception of stimuli after prolonged exposure to a specific stimulus 
. As a consequence subsequent perception is biased. Such a bias is termed after-effect and can occur for different perception modalities. Visual after-effects have been demonstrated for low-level features such as color or motion, as well as for rather complex stimuli such as faces. After-effects that are independent of changes in low-level features are referred to as high-level after-effects. Their occurrence indicates that the adaptation involves higher visual processing areas. Visual high-level after-effects have been reported for many different facial attributes: identity 
, sex 
, eye gaze direction 
, emotional expression 
, attractiveness 
, ethnicity 
and age 
. Valentine’s (1991) 
norm-based coding model of the representation of faces is often used to explain the visual after-effects found for facial attributes. This model suggests that faces are represented in a multi-dimensional face space. In the center of this face space the average of all faces (prototype) is stored and all possible dimensions that describe a face (e.g., age, race etc.) are arranged like a fan around the center and cross in the prototype. An after-effect can be explained by a recalibration of the prototype 
; the position of the average face on a dimension trajectory (e.g., age) temporarily shifts towards the adapting condition. Subsequently presented faces are then assessed in contrast to the “new” average: The same face is seen as older after the exposure to young faces compared to after the exposure to old faces 
So far, all studies reporting high-level after-effects have focused on the processing of facial attributes in adult faces. However, no study has yet investigated how infant faces are situated within the multi-dimensional face space. At least some dimensions on which a face is represented seem to vary between infant and adult faces. For example, although cuteness and attractiveness both represent beauty, attractiveness is a dimension that more appropriately describes adult faces because it has a sexual connotation. In contrast, cuteness applies specifically to infant faces because it triggers care-taking behavior. Indeed, previous studies showed that the Kindchenschema positively influences careful behavior 
. Participants were better in a fine motor dexterity task when they previously saw infant faces compared to adult faces. Furthermore, likeability ratings of cute infants were higher and the willingness to look at them was stronger compared to faces of adult people 
. While there is one study that reported high-level attractiveness after-effects 
no study has yet examined high-level after-effects for facial cuteness.
Here we aim at establishing whether there are cuteness after-effects for infant faces and if so, whether these after-effects transfer across species. In Experiment 1 participants adapted to cute and less cute human infant faces and subsequently assessed the cuteness of human infant faces. In Experiment 2 participants adapted to cute and less cute puppy dogs, and then assessed the cuteness of human infants, to scrutinize a possible transfer of cuteness after-effects across species. So far, only one study investigated facial after-effects for faces of different species 
. They found a species-specific after-effect for eye-spacing in human and monkey faces. The authors interpreted this finding as evidence for functionally distinct neural populations coding faces of different species and for discrete representations of these faces in the human brain. While these findings speak against a common coding of cuteness for different species, Lorenz (1943) 
emphasized the universality of the Kindchenschema. According to his observations, cuteness may be represented by a species-unspecific coding mechanism, since infant faces of different species are characterized by the same facial features (e.g. large eyes, big cranium, etc). Following this universal concept of the Kindchenschema, facial characteristics that constitute a cute face should apply indiscriminately for different groups of vertebrates such as mammals or birds. Using an adaptation paradigm allows us to investigate whether infant cuteness perception of different species involves a common processing mechanism. If the Kindchenschema is indeed universal, we expect the cuteness after-effect to transfer from faces of puppy dogs to human infant faces.
We conducted two experiments to investigate whether high-level cuteness after-effects occur and whether these effects transfer across species. In order to test the existence of cuteness after-effects participants adapted to cute and less cute human infant faces and assessed the cuteness of subsequently presented human infant faces (Experiment 1). We then investigated whether cuteness after-effects transfer across species (Experiment 2). Specifically, we examined whether the exposure to cute and less cute puppy faces influences the evaluation of cuteness in subsequently presented human infant faces.