Table 1.
List of indicators of a positive human–animal relationship.
| Category | Indicator | Examples of measures | Direction of change | Specificity1 | Key references |
|---|---|---|---|---|---|
| Movement/location | Approach2 | Latency to approach/touch human |  |
Conditional | (22) |
| Direction of movement relative to human |  |
Conditional | (22) | ||
| Spatial proximity | Time in proximity of human |  |
Conditional | (30, 51) | |
| Expressive behaviors | Vocalizations2 | Yapping, purring, chirping, grunting, other low-frequency vocalizations | |
Conditional | (46, 48) |
| Ear posture2 | Relaxed ears | |
Yes | (52–58) | |
| Tail posture | Tail low, or wagging | |
Conditional | (59) | |
| Body posture | Relaxed, laying down near the human | |
Yes | (48) | |
| Facial expression | Muscle movement, change in facial display, closed/half-closed eyes | ? | ? | (60, 61) | |
| Qualitative behavior assessment | Positively valenced factors | |
Yes | (62) | |
| Preference for human2 | Choice or motivation for specific human(s) over other stimuli, memory of humans | |
Conditional | (28, 32, 36, 48, 63, 64) | |
| Characteristics of the interaction | Initiating physical interaction2 | Exposing a body area | |
Conditional | (35, 37, 52, 65) |
| Solicitation behaviors like nudging, scratching, play bow | |
Yes | (66) | ||
| Interaction features | Frequency or duration of physical contact, eye gaze | |
Conditional | (67) | |
| Reaction to human contact | Acceptance of stroking or touch | |
Conditional | (68) | |
| Behavioral synchrony | Temporal synchrony of behavioral exchanges/movement | |
? | (69) | |
| Behavioral matching | Complementarity, reciprocity of behavioral exchanges | |
? | (70) | |
| During or postinteraction effects | Relaxation2 | Duration or shorter latency to rest or sleep, rumination | |
Yes | (55, 71–74) |
| Exploration2 | Secure base exploration | |
Conditional | (26, 50) | |
| Postinteraction behavioral changes | Separation distress2 | Searching behavior, distress vocalizations, or contact calls | |
Conditional | (47, 51, 75, 76) |
| Physiological indicators | Oxytocin2 | Hormone concentration or change | |
Conditional | (77) |
| Heart rate2 | Heart rate beat per min | |
Conditional | (54, 78, 79) | |
| Parasympathetic activity2 | Heart rate variability: high-frequency band, RMSSD | |
Conditional | (54, 78, 79) | |
| Cognitive and neurobiological measures | Cognitive bias | Positive judgment of ambiguous cues | |
Conditional | (40, 80) |
| Neurobiology | EEG, fNRIS, neuroimaging (e.g., MRI, PET scan), postmortem measures |
or
|
Conditional | (37, 81, 82) |
These are general indicators, and their expression may be species-specific. This table aims to stimulate discussion and consideration of the complexity of positive HAR assessment and our current state of knowledge on its assessment.
1
“Conditional”: the presence of this sign could indicate a positive HAR, but may need to be interpreted in conjunction with other indicators or the context (e.g., conflicting motivations).
2
The presence of this sign could indicate a positive HAR, but its absence does not necessarily rule out a positive HAR.