The role of cat eye narrowing movements in cat-human communication

Interspecific communication between domestic animals and humans offers adaptive advantages. While human-directed communication in dogs and other species has been studied extensively, the communicative abilities of domestic cats remain relatively understudied, possibly due to their solitary ancestry. However, emerging research indicates cats engage in human-directed gazing and utilize human cues in tasks. This study focuses on a subtle but common cat behavior—the slow blink sequence—to explore its role in cat-human communication. Anecdotal evidence suggests this sequence, involving half-blinks and eye narrowing, occurs in calm, positive contexts. Eye narrowing, a key component of the slow blink, is also observed in positive emotional displays across various species, suggesting potential significance as a positive emotional signal in cats. The study aims to investigate whether cats respond to human-initiated slow blinks with their own slow blinks (Experiment 1) and whether this interaction influences their approach behavior towards an unfamiliar person (Experiment 2). Understanding the communicative function of cat slow blinks has implications for strengthening the cat-human bond and improving feline welfare.

Several studies have explored interspecific communication in domestic animals, demonstrating their ability to interpret human cues (e.g., dogs responding to human gestures, horses and goats discriminating human emotions). Domestic animals also direct communicative behaviors towards humans, such as human-directed gazing. Research on cats' communication with humans has been limited compared to other domestic species but shows evidence of cats using human-given cues in object choice tasks, employing attention-getting behaviors, using auditory signals (purring), discriminating their names, and displaying specific facial actions in negative emotional contexts. Some studies suggest cats may be sensitive to human emotional cues, altering their behavior based on human emotional valence. These findings collectively highlight the potential for deeper investigation into cat-human communication, particularly concerning emotional signals.

Two experiments were conducted to assess the communicative role of slow blinking in cat-human interactions. **Experiment 1:** Twenty-one cats from 14 households participated, with their owners. Cats were tested in their familiar home environments to enhance ecological validity. Experimenters instructed owners on performing a slow blink, which involved a series of half-blinks followed by eye narrowing or closure. Each cat experienced a slow blink stimulus condition and a no-human interaction control condition. A video camera recorded both owner and cat facial expressions. Cat eye movements (half-blink, blink, eye closure, and eye narrowing) were coded using CatFACS, an anatomically based system for measuring facial actions, with an additional code for eye narrowing. Inter-observer reliability was high (Cronbach's alpha = 0.9). Linear mixed models analyzed the rate of eye movements, controlling for number of cats in the household, cat sex, and cat age. **Experiment 2:** Twenty-four cats from 8 households were recruited via online advertisements. Cats were naive to Experiment 1. The experiment involved an unfamiliar experimenter. A 2-minute baseline was recorded before the trials. The experimenter offered a hand to the cat and either performed a slow blink or adopted a neutral expression without eye contact. Trials lasted 1 minute, followed by an approach invitation stimulus. The number of cat eye movements and approach behavior (approach, neutral, avoid) were coded. Linear mixed models analyzed the number of eye movements, and a Wilcoxon signed-rank test compared approach tendencies across conditions. The methodology controlled for potential confounding factors such as age, sex, and number of cats in the household, and experimental controls such as experimenter and camera positions. Analyses were performed in R and account for the nested nature of the data and outliers were excluded.

**Experiment 1:** The rate of eye narrowing was significantly higher during the slow blink stimulus condition than in the no-human interaction control condition. The rate of half-blinks was also significantly higher in the slow blink condition, particularly for male cats. Normal blinks showed no significant effect. **Experiment 2:** The number of half-blinks and eye narrowing movements were significantly higher during the slow blink stimulus condition than in the neutral face control condition. Older cats showed more eye closures. Cats demonstrated a significantly higher tendency to approach the experimenter after a slow blink interaction compared to a neutral interaction.

The findings provide the first experimental evidence supporting the role of slow blinks in cat-human communication. Cats respond to human slow blinks with their own eye narrowing movements, suggesting mutual understanding of the signal. The increased approach behavior after slow blinks indicates that cats perceive this interaction positively. This aligns with anecdotal reports of slow blinks signaling relaxation. The study's use of both familiar (owners) and unfamiliar (experimenters) individuals delivering slow blinks confirms that this communication transcends familiarity and is generalizable across humans. The use of CatFACS allowed for more detailed analysis of subtle facial expressions than previous studies which may explain the differences in findings concerning sensitivity to human emotional cues. While the study controlled for several variables, limitations such as the naturalistic home environment introduce unavoidable noise. Further research is needed to explore the potential evolutionary basis of slow blinking in cats.

This study provides compelling evidence that slow blink sequences are involved in positive cat-human communication. The findings could be valuable for assessing cat welfare in diverse settings, such as veterinary clinics and shelters, and for enhancing cat-owner interactions. Further research should explore the slow blink's role in cat-cat interactions, investigate the behavior's occurrence in different cat populations, and examine whether this behavior is learned or innate. Ultimately, the detailed understanding of feline communication mechanisms can contribute significantly to improving feline welfare and strengthening the cat-human bond.

The naturalistic home environment, while improving ecological validity, introduced some uncontrolled variations in owner and cat behavior. Experiment 1's variation in owner slow blink execution and cat-owner distance adds noise to the data, potentially masking some effects. Experiment 2's use of a neutral expression without eye contact, as opposed to direct gaze may have influenced the approach behavior, confounding the effect of the slow blink alone. These variables make it challenging to completely isolate the effect of slow blinks themselves and additional experiments are necessary to control for these variations in order to isolate the effect of slow blinking in more definitive ways. Replication in a controlled laboratory setting could address some of these limitations.