Table 3.

Subcategories of environmental test stimuli and their descriptions.

Subcategory	Description
Unrestrained in empty area	The participant dog is let off leash with no human direction or interference in a testing area (not their usual home area), with no other purposeful test stimuli (note: If a human is present, they are not the focal stimulus and the dog had encountered them previously).
Unrestrained in area with stimulus options	The participant dog is let off leash with no human direction or interference in a testing area with multiple environmental stimuli.
Restrained in passive situation	The participant dog is restrained, such as with a leash or crate, in a testing area with no purposeful stimuli presentations.
Sudden visual stimulus	A visual stimulus is made to appear or change suddenly (i.e., quickly and unexpectedly).
Stationary object	A stationary object is presented.
Moving object	An object that moves, either on its own (e.g., robotic) or with human intervention (e.g., dragged on wheels), is presented. The object may become still after a period of moving.
Dog	One or more conspecific(s) is/are presented.
Animal	One or more non-human, interspecific animal(s) is/are presented.
Auditory stimulus	A loud or otherwise salient auditory stimulus is created in the vicinity of the participant dog.
Challenging surface or obstacle	An obstacle or surface (e.g., metal grate, stairs, wobbly surface) is presented.
Environmental walk	The participant dog is walked on leash by a person through a complex and naturalistic (i.e., non-controlled) environment.
Physical stimulus	A physical stimulus is applied to the participant dog.
Other environmental	An environmental stimulus which does not constitute one of the other categories.