Foraging, working memory and action
29 April 2005
In a new line of research focussed on understanding attention, Alistair Smith, Iain Gilchrist and Bruce Hood built a foraging room in the Bristol Cognitive Development Centre.
The optimal search for an item requires the brain to produce search strategies and to remember which locations have already been visited. In humans, the ‘visual search paradigm’ – where individuals react to the presence or absence of a target amongst an array of distractors on a computer screen – has long been used as an experimental analogue for search or foraging in the real world. However, we have recently demonstrated that when individuals actually have to move around a room of distractors to find the target, there are some important differences in performance to that seen in the visual search paradigm.
The foraging room was built to examine the way that adults and children code their movements in space. It consisted of a large square room with switches and lights built into the floor that were controlled by a computer. There were 49 potential locations arranged in a seven by seven grid. Each location contained two light-emitting diodes and a micro switch. Participants were required to search for a target at potential locations indicated by the illumination of only one of the diodes. The participant can 'search' by activating the switch to see if the second diode light up. They were looking for the pair of diodes where only one lit up.
This foraging project was the first pilot study to measure spatial navigation in humans when performing a task that is similar to the Morris water maze
The setup enabled the team to simultaneously present target displays and record the search behaviour of an individual as they moved around the room activating switches to find the unlit target. As such, this foraging project was the first pilot study to measure spatial navigation in humans when performing a task that is similar to the Morris water maze, a task frequently used to study spatial representation in the rat.
They tested adults and children, as well as a few individuals with Williams Syndrome, a rare disorder that, like Down's Syndrome, is caused by an abnormality in chromosomes. This clinical group are currently the focus of interest from behavioural geneticists who are trying to determine the genetic influences of spatial coding in the brain and the foraging paradigm has clearly demonstrated the role of specific gene deletions in this group. The Williams work is being pursued in collaboration with Annette Karmiloff-Smith at the Institute of Child Health in London who is one of the world experts on this condition..
Meanwhile, he findings from normal adults revealed that foraging shared many similarities with standard visual search tasks where the individual has to find a target among distractors on a computer screen. However, there were some important differences in that individuals were more strategic and relied more heavily on memory when in the foraging room. This appears to reflect the cost of making an error in a real environment, compared to a computer screen set-up. They found this same effect in children who tended to make more errors (by re-checking the same location more than once) than adults. Interestingly, the same child made more errors when they had to use the non-dominant hand to activate the switch, indicating that the use of a hand that requires more effort interferes with memory on this task. Smith believes that this reflects the competition of resources for controlling the non-dominant hand and keeping track of where you have been.
There is still much more to do with the room. Hood and his team have just received three years of further funding from the Medical Research Council to continue and extend this research in new directions – they just have to remember where they have been!