Finding a route to independence
Navigation – the ability to find our way through large-scale space – is one of our everyday activities. We take for granted that we can travel to work, navigate the aisles in a supermarket. Yet for individuals with neurodevelopmental disorders such as Down Syndrome and Williams Syndrome, poor navigation abilities can limit their independence.
Over the last decade my collaborators and I have been working with people with Williams Syndrome, and lately people with Down Syndrome as well as other neurodevelopmental disorder groups. We’ve been seeking to determine how well these individuals are able to navigate, whether their navigation strategies differ from the strategies observed in the typical population, and what factors might be limiting their ability to find their way. In doing so, we have learnt not only about atypical development, but have gained important insight into the typical development of navigation skills.
Let’s start by exploring navigation itself. Siegel and White (1975) proposed three sequential stages. The first stage involves gaining knowledge of the landmarks in their environment; the second stage refers to knowledge of the turns and landmarks along a route. The use of this landmark knowledge and route knowledge enables us to remember a fixed route from A to B. This strategy, whilst effective, is limited because it is inflexible to change if the route becomes unavailable, for example if access is blocked. Individuals who rely on route knowledge alone are vulnerable to getting lost because they are not able to re-orient themselves if they deviate from their known route.
A more sophisticated type of navigation, Siegel and White’s third and final stage, involves developing an understanding of the configural structure of the area – knowledge of the spatial relationships between routes and landmarks within an environment. This is known as the development of a cognitive map, or configural knowledge. Configural knowledge facilitates a more flexible strategy; it enables us to find alternative routes, or shortcuts and provides us with adequate knowledge to re-orient ourselves if we get lost. In typical development, the development of a cognitive map begins to emerge between the ages of 5 and 10 years (Broadbent et al., 2014; Bullens et al., 2010).
It is the development from route knowledge to configural knowledge which reflects qualitative change in development. This is because individuals start to integrate knowledge of learnt spatial locations to form a cognitive map (see Montello, 1998). This qualitative difference is also demonstrated with respect to what are known as spatial frames of reference. Landmark and route knowledge reflect the use of an egocentric frame of reference: we encode the location of a landmark relative to ourselves, and use a viewpoint-dependent representation. In contrast, the development of configural knowledge and a cognitive map requires us to use an allocentric frame of reference: we encode the locations of objects relative to other objects or elements of the environment, and this is viewpoint-independent (see Burgess, 2006). This difference is also supported at a neural level; in adults, route knowledge activates the caudate nucleus, whilst configural knowledge activates the hippocampus (Hartley et al., 2003).
Williams syndrome (WS) is a rare genetic disorder with a prevalence of between approximately 1 in 7,500 (Strømme et al., 2002) and 1 in 20,000 (Morris et al., 1988) live births. Down syndrome (DS), also a genetic disorder, has a prevalence of between 1 and 3 per 1,000 live births (de Graaf et al., 2011). Both groups are classified as having moderate learning difficulties, yet they present with contrasting cognitive profiles of poorer spatial than verbal abilities in WS (Farran & Karmiloff-Smith, 2012), and the opposite pattern in DS (Klein & Mervis, 1999). With reference to navigation, despite these different uneven cognitive profiles, both groups have atypicalities in the hippocampus, in terms of structure and function (Pinter et al., 2001; Meyer-Lindenberg et al., 2004). Coupled together, this suggested to us that configural knowledge was likely to be impaired in both DS and WS, and that navigation performance would draw on differing underlying mechanisms
We have carried out studies in both the real world and virtual environments. In our first study with people with WS, we used a University campus as a safe real-world environment to measure route knowledge and configural knowledge in individuals with WS (Farran et al., 2010). Participants were led around a one-kilometre circular route and were then asked to walk the route themselves, guiding the experimenter. We measured route knowledge as the proportion of correct turns made. To measure configural knowledge, we stopped participants at four points on the route and asked them to point towards three landmarks that were on the route, but not currently visible.
In line with our predictions, the WS group were able to develop route knowledge, but not configural knowledge – they made the correct turns, but couldn’t point towards the landmarks. This suggests that in everyday life, this group are reliant on fixed and inflexible routes. This has strong implications for independence and confidence, and is likely a contributing factor to why only 7-12 per cent of adults with WS are in independent work (Stinton & Howlin, 2012).
Poor configural knowledge also limits the spatial tools that individuals with WS can use to help them to find their way. That is, we have also found that maps are difficult to use for many people with WS (Farran et al., 2010; Broadbent et al., 2014). This is likely because maps rely on an understanding of the spatial relationships between places (i.e. configural knowledge). More recently, we asked individuals with WS about their strategies when they get lost. 83 per cent of individuals with WS ask someone to help them to find their way. This compared to a smaller percentage of individuals who would use landmarks (42 per cent) or maps (3 per cent). Similarly, when they get lost, 68 per cent of respondents with WS ask a safe person compared to 26 per cent who would ‘think and look’, i.e. use their spatial skills to re-orient themselves (Farran et al., 2016).
As for people with Down Syndrome, they appear to have poor route knowledge, making more errors when learning a route than individuals with intellectual disability and a typically developing (TD) group who were matched by mental age (Davis et al., 2014). Researchers have shown participants with DS a virtual maze, and asked them to use the landmarks in the environment to locate a hidden blue rug in a central arena (Pennington et al., 2003; Edgin et al., 2010). This is a measure of configural knowledge. Performance of the DS groups was at the level of 3- to 8-year-old TD children, and Edgin’s study also reported that many with DS could not complete the task.
This suggests that, as in WS, configural knowledge is difficult to acquire for individuals with DS. Also similar to WS, the tools that facilitate the development of configural knowledge in the typical population (e.g. providing a map, and learning a route from an aerial, map-like view, rather than a first-person perspective) are also not beneficial to people with DS (Meneghetti et al., 2017; Toffalini et al., 2018).
Which patterns of performance are syndrome-specific, and which are artefacts of having learning difficulties? We addressed this by comparing across syndromes, using virtual reality in a series of studies. Virtual reality is less physically demanding than the real world; participants can be given extensive experience of a carefully controlled environment in a relatively short space of time. Moreover, it is not subject to the weather patterns or changes in seasons, which can change an experience of a route. Importantly, virtual environments tap into the same cognitive mechanisms as real-world environments (Richardson et al., 1999; Coutrot et al., 2019).
We compared route knowledge across TD children, individuals with WS and individuals with DS. Importantly, all participants could gain route knowledge. However, route knowledge in the DS group was significantly poorer than in the TD and WS groups (Purser et al., 2015). We also discovered that the impairment in DS was related to non-verbal ability, with poor non-verbal ability being disproportionately detrimental to route knowledge in DS compared to the TD or WS group (Purser et al., 2015). Evidence that individuals with DS have some difficulties recognising landmarks (Toffalini et al., 2018) might also contribute to this. With respect to WS, we have shown that individuals with WS have an unusually strong reliance on landmarks when acquiring route knowledge (Broadbent et al., 2014), but that the ability to discern which landmarks are useful is dependent on level of non-verbal ability – those with lower non-verbal ability do not differentiate between useful and less useful landmarks (Farran et al., 2012). Furthermore, using eye-tracking, we demonstrated that individuals with WS attend to landmarks which don’t help them acquire route knowledge – for example, standard streetlamps (Farran et al., 2016).
Using virtual reality, participants can retrace routes numerous times. In this way, our finding of impaired configural knowledge in WS was later supported by Broadbent et al. (2014), who used a virtual environment cross-maze (a square maze with four radial arms). In this task, after a familiarisation phase, participants were asked to find the shortest route to one of four exits. Whilst typically developing 5- to 10-year-olds showed developmental progression from an egocentric route-based strategy to a configural strategy, the WS group often took inefficient routes to reach the required exit.
In our recent study, we compared configural knowledge in those with DS and those with WS (Farran et al., 2015; also see Courbois et al., 2013a). Participants were asked to learn two routes, A to B and A to C, within a grid environment. Having learnt these routes, they were then asked to demonstrate a short cut from B to C. Their ability to find the short-cut was our measure of configural knowledge. We demonstrated that 59 per cent of TD 5- to 11-year-old participants could find the short-cut. This compared to only 10 per cent of individuals with DS and 35 per cent of individuals with WS. In fact, the DS group often used the strategy of simply adding the two known routes together, which requires no configural understanding at all. Whilst configural knowledge was strongly related to non-verbal ability in the TD group, it was related to attention switching in the WS group (correlations were not useful in the DS group due to the low success rate).
We suggest that the WS group are limited by their ability to switch from their first-person or egocentric perspective to the allocentric, viewer-independent perspective required to hold a cognitive map and to make decisions based on the configural structure of the environment. As mentioned above, individuals with DS do not benefit from learning a route from an aerial perspective (where arguably no switching is required) (Toffalini et al., 2018), which suggests that the limitation for individuals with DS differs from the limitations observed in WS. Our current ongoing research will provide insight into any possible group difference in the ability to use an aerial view during a configural knowledge task. We will look at the benefits of providing a sat-nav style map while participants are navigating from a first-person perspective, and see whether – as we might expect – this helps a WS group more than a DS group.
Implications for independence
Navigation is vital for independence yet, until recently, little was known about the ability to acquire these skills in DS or WS. Both route knowledge and configural knowledge are poorer for individuals with DS than for individuals with WS. Despite this individuals with WS and DS can learn a route in a novel environment, albeit after a lot of practice (particularly if they have low non-verbal ability). Given the importance of landmarks for route knowledge, we suggest that individuals with WS would benefit from tuition on what landmarks are useful and why. Landmark usefulness has not been investigated in DS, but we do know that poor landmark choice is also observed in individuals with intellectual disability (Courbois et al., 2013b). This suggests that the benefits of training on landmark usefulness could extend beyond those with WS.
Configural knowledge is not achieved by the majority of individuals with DS or individuals with WS. This has strong implications for independence, because routes are not always predictable; a route might be blocked, or a bus might take a detour. Without configural knowledge it is difficult to re-orient oneself in these situations. Strategies such as using a map are unlikely to be beneficial for these groups without training. People with DS or WS, therefore, need to be provided with strategies such as having a person to phone, or training to look for a particular distant landmark when lost, or training on how to use maps. Furthermore, we have also shown that individuals with WS can use their relative strength in verbal ability to positive effect by verbalising a route while they are learning it (Farran et al., 2010). It is also possible that training in more basic skills, such as non-verbal ability (both groups) or attention switching (WS specifically), could have downstream benefits to the ability to navigate.
Emily Farran is Professor of Developmental Psychology at the University of Surrey
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