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An ordinal timing system

University of British Columbia

In this series of Experiments we examined the behaviour of laboratory rats in a daily time-place learning task. The rats received two daily sessions (one at 09:30, and a second at 15:30) in a large, clear, test chamber. A lever was mounted on each of the four chamber walls. Each rat could work for food on one lever during 09:30 sessions and on a different lever during 15:30 sessions. Over the course of Experiment 1 the rats clearly learned which lever would provide food during 09:30 and 15:30 sessions. In Experiment 2, we examined the affect skipping 09:30 and 15:30 sessions had on the rats' time-place behaviour. In the 09:30 sessions which followed a skipped 15:30 session the rats continued to expect food at their 09:30 levers. However, in the 15:30 sessions which followed a skipped 09:30 session the rats incorrectly expected food at their 09:30 levers. These results suggest that; (1) receiving a 09:30 session, and not the passage of time, was necessary for the rats to anticipate the location of food in 15:30 sessions, and (2) receiving a 15:30 session was not necessary for the rats to anticipate the location of food during 09:30 sessions. These results suggest that the rats' learned to press one lever during their first session of each day and to then press a second lever during their second session of each day. We called this a daily route strategy. As the rats' time-place behaviour was not disrupted when 15:30 sessions were skipped, some event other than 15:30 sessions must have been capable of resetting the rats route each day. In Experiment 3 we determined where the rats expected food during probe sessions at 11:45, 13:00, and 14:15. At 11:45 the rats mainly pressed their 15:30 levers. This is also consistent with the use of a daily route strategy. However, at 11:45 the rats pressed their 15:30 levers relatively less, and they pressed the two levers which never provided food relatively more, than they did during baseline 15:30 sessions. This effect was also evident in the probe sessions at 13:00 and 14:15, but it's magnitude decreased the closer the probe session was in time to 15:30. This result suggests that a second timing system had weak, but detectable, control over the rats' time-place behaviour. In Experiments 4a&b we demonstrated that the rats did not solely rely on the daily transitions of the colony light-dark cycle to reset their route each day. Additionally, in Experiment 4c we demonstrated that the rats did not solely rely on the occurrence of either the transitions of the colony light-dark cycle or a 15:30 session to reset their daily routes. Later, Experiment 5 showed that the occurrence of a 15:30 session was not even sufficient for the rats to reset their daily routes. We suggest that the rats reset their daily routes when a food-entrained circadian phase timer attained some fixed phase angle each day. We also propose that the daily route employed by the rats in the present time-place learning task is an exemplar of ordinal timing ~ the knowledge of the order of a set of events within a period of time. We contrast the temporal information provided by ordinal timing with that provided by the more well known phase and interval timing. We then suggest that ordinal, phase, and interval timing provide animals with representations of time at the ordinal, interval, and ratio levels of measurement respectively. Finally, we suggest that animals posses these three timing systems because each system is specifically adapted to enable animals to anticipate a specific type of spatiotemporal regularity.

Thesis/Dissertation

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2009-02-06

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http://hdl.handle.net/2429/4281

Psychology

University of British Columbia

UBCV

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