Spatial cognition: the representation of three-dimensional space
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1
University of Oxford, Department of Zoology, United Kingdom
To navigate around its local environment, animals must recognise their own position with respect to their goal. This task can be completed successfully if animals have a representation of space in their brain, built upon learning and remembering environmental features. Previous research has focused on the cues animals encode from the horizontal dimension, either over planes or by use of ground cues from the air. However, most animals need to move vertically, hence, their internal representation of space should include information pertaining to the vertical axis. Despite this, we know virtually nothing about the cues that animals use in this dimension.
Free vertical movement is exemplified by flying or swimming animals, which can move with six degrees of freedom (unlike surface constrained animals that can only move with three). This increase in vertical movement increases the potential difficulty of a navigational task. Here, we consider how pelagic fish might overcome this problem.
Using a novel assay based on associative learning of the vertical and horizontal components of a three-dimensional Y-maze placed in a large tank, we found banded tetra fish (Astyanax fasciatus) learned and remembered information from the vertical and horizontal components when presented either separately or as an integrated three-dimensional unit. When information from the two components conflicted, fish used the previously learned vertical information in preference to the horizontal, showing a separation of the two axes of space in their representation of space. This separation was found both in the presence and absence of surrounding visual landmarks, and could simplify the problem of encoding three-dimensional space.
These results suggest that, for fish, the vertical axis contains particularly salient spatial cues. Hydrostatic pressure is a global cue in aquatic environments that could be harnessed by fish to determine their vertical position. We have developed a theoretical model whereby fish could use the fractional rate of change of swim-bladder volume, caused by changes in hydrostatic pressure during vertical movements, to inform them of their absolute depth. Behavioural and neurophysiological studies have shown that fish have the ability and apparatus to detect changes in swim-bladder volume, and empirical studies will reveal whether fish use this cue to navigate in the vertical dimension.
Building from this, we considered how these separate elements are integrated when fish navigate through full volumetric space. We trained fish to swim toward a reward in a three-dimensional Y-maze before removing the arms of the maze in probe trials and digitally tracking the fish while they swam freely through the volume. Our results suggest not only that fish are able to accurately encode metric information in a volume, but also that the error accrued in the horizontal and vertical axes of space whilst navigating is very similar. While the components of space are separated under a forced choice trial, when fish are allowed to swim freely they use information from both axes equally. This contrasts with animals that are constrained to surfaces whilst moving through a three-dimensional environment, which show higher accuracy in encoding the horizontal component.
Keywords:
fish,
Hydrostatic Pressure,
navigation,
Orientation,
spatial cognition,
swim-bladder,
three-dimensional
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Invited Symposium (only for people who have been invited to a particular symposium)
Topic:
Orientation and Navigation
Citation:
Holbrook
RI and
Burt De Perera
T
(2012). Spatial cognition: the representation of three-dimensional space.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00027
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Received:
26 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. Robert I Holbrook, University of Oxford, Department of Zoology, Oxford, Oxfordshire, OX1 3PS, United Kingdom, 309385@frontiersin.org
Dr. Theresa Burt De Perera, University of Oxford, Department of Zoology, Oxford, Oxfordshire, OX1 3PS, United Kingdom, theresa.burt@zoo.ox.ac.uk