A track scent is often a mixture of both the air scent and the ground scent being left behind by an individual. Dogs are able to determine a track scent by identifying a combination of both human odours and environmental odours released by an individual. They then use the strength of this overall scent to determine the directionality of a trail and track along that route. Since an initial footstep is much less potent than the last footstep taken by an individual, dogs move in the direction where the scent seems to become stronger. Additionally, dogs have been observed to alternate between visual tracking and scent tracking depending on the circumstances of their environment. For the most part dogs prefer to use olfactory cues even when the target or visual cues are within their line of sight. However, there has been research conducted where dogs have been shown to rely on visual, social or cognitive cues to identify the tracks of an individual.