103_19_full - PSYC 103 Winter 2011 Lecture 19 Feeding...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: PSYC 103 Winter 2011 Lecture 19 Feeding Relative numerosity discrimination Control for time Control for number •  Rats are sensitive to time and number Are time and number coded together? Time vs number Case 1 Case 2 Conditional time/number discrimination with flashing colored keys: •  if Green, then peck left for 2 flashes, right for 8 flashes, regardless of duration •  if Red, then peck left for 2 sec, right for 8 sec, regardless of number of flashes • Test with 2-8 pulses over 4 sec (counting), or 4 pulses lasting 2-8 sec (timing) Timing at chance counting at chance Foraging Foraging: outline 1.  What to do in a simple environment of unchanging patches 2.  What to do if those patches change 3.  Where to forage when in a group 4.  What to forage on Foraging as an “optimal” behavior Assumption: behavior is selected to maximize (i.e. optimize) fitness Operational currency: some measurable correlate to fitness (e.g. energy expenditure) Characterization of conditions: general constraints of foraging behavior Goal: Optimal foraging •  minimize energy expense during foraging •  maximize energy gain from foraging Schedules of reinforcement Schedules of reinforcement: rules that defines which occurrences of the instrumental response are reinforced; primary determinants of behavior • Ratio Schedule: The number of responses determines reinforcement • Interval Schedule: The timing of the response (since the last reinforcer) determines reinforcement Ratio Schedules The number of responses (since the last reinforcer) determines reinforcement; the time between response does not matter Fixed ratio (FR): required number of responses is constant Variable ratio (VR): required number of responses varies between reinforcer deliveries “Break-run” pattern Interval Schedules The passage of time determines the availability of reinforcement; the number of responses made during the interval does not matter. Fixed Interval (FI): required interval is constant Variable Interval (VI): required interval varies between reinforcer deliveries FI scallop Typically, once the interval expires the animal must make one response Interval schedules produce lower rates of responding than ratio schedules Deciding where to forage Resources occur in clumps, or “patches”, separated by empty (resource poor) space. Some patches are likely better than others, but how do you choose? Must be concurrent VI schedules Responding on a “random ratio” schedule Reinforcement occurs on random subset of trials, some fixed percentage of time (e.g. on average 35% of responses are reinforced) Strategy: Sample then choose best response Decision = Point at which animal chooses response > 90% of time Animal adopts “steady state” response Fluctuating patches Sampling behavior tracks changes in the environment (patch abundance) When the fluctuating patch is good, pigeons tend to choose it until it goes bad again When the fluctuating patch is bad, pigeons tend to choose the stable patch more often Sampling frequency is inversely proportional to reinforcement probability in the constant patch Foraging models •  Maximize reinforcers?: do animals choose the option the has the highest probability of payoff at a given point in time -- no. •  Scalar expectancy theory (SET): choice between reward probabilities is a choice between delays to to food. Different delays (intervals) are remembered, and the animal samples from the distribution of remembered delays. FI4 VI4 Concurrent FI4 VI4 Equal payoffs More short intervals will come from this memory Maximizes rate under psychological constraints Choosing patches in a group ? 1 10 Ideal free distribution: The distribution in which each individual can maximize its intake under ideal conditions (perfect information, equal competitiveness); a perfect “match” Under-match Individual learning The proportion of individuals at a patch quickly comes to match the prey density 1 2 Initial match to rates of throwing Subsequent match to size of bread Note: the distribution of ducks stabilizes before individuals have a chance to visit more than one patch What happens when patches deplete? Successive prey items take longer and longer to find: When do you give up and leave? Marginal value theorem (MVT): Forager should stay at the patch until the rate of energy intake falls below the average in the habitat. After this point, it could do better elsewhere. MVT implies that animals track rate of intake and overall quality of environment 2. Giving up time was longer in the poor environment (consistent with MVT) Giving up time 1. Giving up time is constant within each environment, regardless of patch quality Remembering and Averaging time MVT implies accurate representation of time in the patch and travel time between patches •  Train starlings to feed from a recognizable location •  Vary patch depletion (rate of dispensing) and location of feeding station Behavior follows prediction from MVT: the longer the round trip, the more meal worms collected Remembering and Averaging time •  When pecking, variable numbers of prey are dispensed at fixed intervals, until “patch” depletes •  Starling must fly between perches several times to reset patch (i.e. fly to new ‘patch’) Pecking rates peak at the value of the inter-prey interval (and scale with magnitude) as for peak procedure What about giving up time? Giving up scales with inter-prey interval too! Longer inter-prey interval lead to slower giving-up (following Weber’s law). Prey selection Cycle of events Handling requires time…time not spent feeding Task: find items that maximize energy per unit of handling time (E/H) When times are good (lots high E/H items): be choosy When times are bad: take what you can get. In general, prey selection follows other models of choice (e.g. SET, delay reduction hypothesis) in minimizing the delay to food Concepts 1.  2.  3.  4.  5.  Evolution can produce simple rules for doing complex things, that do not require theoretical computations or explicit representations of variables Most environments vary across time and space. Optimal decision making may require information about the whole environment drawn from samples and memory. The time available for foraging is usually limited, best strategies may change as time runs out. Information about time intervals is vital. Some animals use threshold change, others represent and remember time intervals. Ideal (optimal) behavior is always constrained by the psychology and biology of the organism. ...
View Full Document

Ask a homework question - tutors are online