DOI: 10.5255/ukda-sn-855171
title: Flexible and Habitual Mechanisms of Human Navigation, 2016-2019

description: The project concerns both the psychological and neural mechanisms involved in flexible and habitual forms of spatial learning. Traditionally it has been thought that flexible navigation is based upon a map-like representation of a person’s environment – a cognitive map - and that this representation is subserved by the hippocampus. The cognitive map is thought to integrate the relations among stimuli in an environment so that a route through the environment can be planned without having to have direct experience of that route. In addition, influential theories of spatial learning argue that the formation of a cognitive map, based on some parameters around cue type or environmental stability, is incidental – occurring as a person encounters new stimuli, regardless of prior learning experience. Our starting point for our project was to test both the notion of incidental learning in flexible spatial learning, and to determine if a hippocampus-based cognitive map was only one function of the hippocampus in spatial learning, testing if it is also involved in non-mapping functions that involve complex representations of prior and future events and their relations to one another. We conducted a series of spatial learning experiments in which participants control a first-person perspective navigating around and environment. Generally, control was via keys on a computer keyboard and the participant sat a short distance away from a computer screen. In our first output we tested two theories of incidental spatial learning by testing whether certain spatial cues, or environmental stability, created an immunity for spatial learning to be susceptible to a form of cue competition known as blocking. Blocking occurs when prior learning to a cue prevents subsequent learning to an added cue and is the hallmark of associative learning theory. This is because associative learning algorithms rely on prediction error to explain learning, meaning that new learning only occurs when prediction error is high. Incidental learning should occur regardless of prediction error, so some theories of spatial learning predict that blocking will not occur. Our results found no evidence for incidental learning based either on cue type or on environmental stability. Another form of cue competition is overshadowing, when concurrent learning based on two or more cues limits learning based on each, compared to a condition in which learning is based on only one cue. In two sets of studies we examined overshadowing of both boundary cues, which have been argued to be immune to cue competition, and environmental geometry, which has been the subject of a similar claim of modularity. In both studies we found positive evidence for overshadowing, undermining the claim that cognitive mapping is immune to cue competition. Further to our studies of learning based on boundaries and geometry we examined the effects of these parameters on memory for object locations. We found that manipulating these parameters had a profound effect on how participants remembered the locations of objects they had encountered, which may have important implications for theories of episodic memory. The strand of our study examining non-mapping navigation memory was served by two major fMRI studies. Processing of one study was delayed by the Covid-19 pandemic so we are unable to provide those data as yet. The other was designed to observe the activation of the hippocampus and caudate putamen when participants learned their way through a high-sided maze. They could rely on objects they encountered on their way or the sequence of turns, but they could not readily map the environment. We found evidence for caudate putamen activation when behaviour was under the control of landmarks, but evidence for hippocampus activation when behaviour was under control of the sequence. In a subsequent behavioural study we found evidence that sequence learning was still susceptible to blocking. The basis of the second fMRI study was the under-studied effect of reversing a route that was previously learned. In two behavioural studies we examined whether under- or over-training an outward route affected a participant’s ability to reverse their steps, as well we examining the effects of individual differences in spatial wayfinding strategies and behavioural inhibition on reversing a route. Routes could be learned based either on the identity of a landmark at a junction or the sequence of turns taken to reach a goal location. The parameters determined from the behavioural studies formed the basis of the fMRI study, as well as the parameters for a similar behavioural study in which a realistic rendering of a university building was developed. This strand is designed to broaden the scope of our research for more applied work in the future.