Biological Basis of Behavior Lecture 6: Forgetting and Remembering (PDF)

Lecture 6: Forgetting and RememberingPSY2304Biological Basis of Behaviour Forgetting•Nature of forgetting: Target memories could be lost because of –Proactive interference from information acquired PRIOR to target–Retroactive interference from information acquired AFTER target–Decaydue to the passa...

Lecture 6: Forgetting and RememberingPSY2304Biological Basis of Behaviour Forgetting•Nature of forgetting: Target memories could be lost because of –Proactive interference from information acquired PRIOR to target–Retroactive interference from information acquired AFTER target–Decaydue to the passage of time.–We’ll consider evidence for each of these mechanisms for forgetting Delayed matching to sample (DMTS)•Modern, Skinner-box technique for studying delayed reaction•Despite the name, does not necessarily require recognition of identity of sample and comparison stimuli •Many variations: –oddity from sample-choose the comparison that does not match –symbolic matching to sample(DSMTS): comparison stimuli are not the same as the sample, and the subject must learn the "code" connecting them–multiple samples -in which case the design becomes a test of recognition memory or a list recognition task •Used with pigeons, monkeys, dolphins, etc Proactive interference•Grant and Roberts (1973)•Ordinary DMTS on some trials•Other trials two samples are presented -either 10 sec or 0 sec apart.•Animal must respond on basis of last sample.•Result is that performance in the 0 sec condition, when one sample is immediately followed by the other, is worse.•This is good evidence for proactive interference in DMTSdelay Retroactive interference•Grant (1988)•Ordinary DMTS•On some trials the brightness with which the chamber is illuminated is increased during the delay between sample and comparison.•Result is that performance in the increased illumination condition is worse.•Is this good evidence for retroactive interference in DMTS? I’m not entirely convinced.delayChamber illumination increased (or not) The Radial Arm Maze•Radial Arm Maze experiments with rats.•A means of presenting a list of items to the animal.•In early experiments animals allowed to run down n (freely chosen) arms then removed for a delay interval then returned on test.•Later experiments control the arms experienced on the study phase. DOOR FOOD WELL CENTRAL PLATFORM Choice accuracy in a free choice procedure in an 8-arm radial maze.Choice number2345678Observed %100999896979080Data from Olton and Samuelson (1976).Early work in the Radial MazePerhaps the most striking aspect of these results is that performance is so good. But a free choice procedure suffers from the possibility that this is not so much due to memory as due to stereotyped response patterns on the part of the animal, e.g after exiting an arm, turn left and take the next one. ??A 2 A F C procedure after forcing the animal to visit a set of randomly chosen arms (shown in blue). The animal is given a choice between two arms, one visited and one novel, and required to choose the novel one. In this experiment the eight arms of the radial maze were partitioned into two sets, A and B, of four arms each, then an initial phase of exposure to the arms in B was given, followed two hours later by a study phase in which the rats were forced to the arms in A. After a further two hours a test phase of free choices amongst all eight arms was given, with choices of the B set rewarded. A control group did not get the initial interference phase. Experimental animals performed worse than controls, indicating a PI effect of the initial exposure to the B arms.Proactive Interference: Hoffman and Maki (1986)Exposure2hrsStudy 2hrsTest In this experiment the eight arms of the radial maze were again partitioned into two sets, A and B, of four arms each, then an initial phase of exposure to the arms in B was given, followed by running 3 other similar mazes in different rooms to the test maze. Finally the animal was returned to the test maze and its performance in choosing the A set of arms was found to be worse than that of controls who had experienced the same delay between the initial phase and test, but not run the intervening mazes.Retroactive Interference: Roberts (1981)StudyInterpolated mazesTest This experiment used the basic 2AFC procedure already described. Animals were forced to either 1, 3, 5 or 7 arms of the maze then given a choice between a visited and an unvisited arm. The results for the 3, 5 and 7 arm conditions were plotted in terms of backward serial position, where 1=last arm visited (hence the same delay between study and test in all conditions) and 2= second last visited etc. Thus, for the 3 arm condition 3 would be the first arm visited on that trial whereas for the 5 arm condition it would be 5. Given that the rats run at a roughly constant rate in the maze (arms/min) this means that if elapsed time is the only factor the backward curves should superimpose. Within the limits of statistical error Roberts and Smythereported that they did (see next slide).But there’s a slight problem. This result can be explained using decay (time), but it could also be driven by number of arms visited after the arm tested, an interference account. At the moment, there’s no way of telling which is responsible. The next slide sorts this out.Decay: Roberts and Smythe (1979) 012345670102030403 arms5 arms7 armsBackward serial positionFrom Roberts & Smythe (1979)% Errors The nature of the code in memory:Retrospective or Prospective?Retrospective = e.g. remembering the arm just visited.Prospective = e.g. remembering the arms you have yet to visit.Animals can definitely use retrospective encoding, the question is: can they employ a prospective code and can they switch between the two codes in a flexible manner?Coding Delayed symbolicmatching to sampleNotice:–the issue of identity of the sample and comparison stimuli does not arise in this case–There are two different discriminations (between samples and between comparison stimuli). This was exploited by Roitblat. DMTS Roitblat (1980) Sample (one per trial) Comparison (all available) Blue 0º Orange 12.5º Red 90º Roitblat’s result is that the animals make more mistakes -make more confusions -when Blue and Orange are the sample. That is, they tend to give the correct response for Orange to the Blue sample and vice-versa. They make less confusions on trials where the sample is Red, even though some confusion with Orange might be expected. This suggests use of a prospective code. Cook, Brown and Riley, 1985 Cook, Brown and Riley (1985,JEP:ABP, 11, 453-469) produced evidence that suggested that rats could switch flexibly between retrospective and prospective codes. They used a 12 arm maze, but I’llreport my replication of these experiments with an 8 arm maze.Rats were forced to either 2, 4 or 6 arms of the maze (Cook et al used 2, 6 or 10), then taken out for 15 min., and then tested on a visited vs. an unvisited arm. On the left is a study phase set of 4 arms… Which arm of the two shown was the unvisited one??? 2 4 6 20 30 40 No. of visited arms % Errors McLaren (1990): Results from an 8 arm radial maze with 15 min. retention interval. Note that more errors are made in the 4 arm condition than the 6 arm condition. Cook et al (1985) reported a similar finding coupled with a serial position effect in the conditions that showed the highest error rate, whereby the arms entered early in a trial were more likely to be (incorrectly) revisited after the delay. They argued that this indicated a switch from a retrospective code to a prospective code at the appropriate list length. Coming next week:Space (with a lot more about spatial learning and memory) –and a bit about navigation Articles cited not already given•Roberts, W.A. and Smythe, W.E. 1979. Memory for lists of spatial events in the rat. Learning and Motivation, 10, 313-336•Roitblat, H. L. (1980).Codes and coding processes in pigeon short-term memory.Animal Learning and Behavior, 8, 341-351. Reading•Pearce 3rd Ed. Ch. 8 &9.•Pearce 2nd Ed. Ch. 6