Numerical competence in animals: Outline Why is this question interesting? Levels of numerical competence Numerosity discrimination rats discriminate numbers of stimuli or responses Brannon & Terrace s monkeys (reading and web) Using number symbols (numerons) Sheba the chimpanzee (video) Spontaneous counting and adding of small quantities by monkeys and babies (video) Theories, evolution, development (next time) Psy 362S 2007, Lecture 9.1 slide 1 But first a little more on transitive inference and distance effects Serial order learning, tests with pairs of items: Latency to choose vs. position of first item And how many items between 1st and 2nd items Monkeys show effects of distance, pigeons do not. Psy 362S 2007, Lecture 9.1 slide 2 Monkeys & pinyon jays show distance effects in transitive inference: 1. More accurate with greater interitem distance Psy 362S 2007, Lecture 9.1 slide 3
Distance effects in transitive inference: 2. At a given interitem distance, longer to decide (and less accurate) with pairs later in the series Social pinyon jays show this effect but less social scrub jays do not. Monkeys also show it and pigeons do not. Psy 362S 2007, Lecture 9.1 slide 4 Social transitive inference in cichlid fish: a few more details Bystanders preferred the weaker fish of a pair (A vs. E or B vs. D) both in the familiar tank and in a novel context (grey and white bars), Psy 362S 2007, Lecture 9.1 slide 5 Levels of numerical competence 1. Subitizing 2. Numerosity discrimination 3. Counting 4. Concept of number: arithmetic Research questions How is counting related to numerosity discrimination? In evolution? In development? Which of these is shared across species and which are specifically human? Psy 362S 2007, Lecture 9.1 slide 6
Numerosity discrimination 8 pulses of tone Ë press left lever 2 pulses of tone Ë press right lever Problem:Duration and number confounded 2 pulses : z z 8 pulses: z z z z z z z z So maybe the rat is timing the stimuli Test with times equated (all 4 seconds long) 2 pulses : z z 8 pulses: z z z z z z z z Psy 362S 2007, Lecture 9.1 slide 7 Tests with constant duration of stimulus 100 % choice of 8 lever 50 Where is 50:50? 0 2 3 4 5 6 7 8 number of tone pulses Psy 362S 2007, Lecture 9.1 slide 8 Weber s law in numerosity discrimination The task: press Lever 1 N times, then 1 press on Lever 2 will be reinforced. Psy 362S 2007, Lecture 9.1 slide 9
Brannon and Terrace reading Monkeys had learned serial order tasks Trained with numerical sequences E.g. touch 1-2-3-4 Link to more on the web Many stimuli used in training More new stimuli in the test Most important: Trained with 1-4 but transfer to 5-9 Psy 362S 2007, Lecture 9.1 slide 10 Which has more? Latency and accuracy depend on the difference. Same for people and monkeys. (see also Brannon & Terrace, figure 4) Psy 362S 2007, Lecture 9.1 slide 11 What is counting? Subject applies tags, or numerons e.g one, two Anything can be counted (generality) Have to test counting with novel items Cardinality Last tag = number of items in the set Sheba the chimpanzee; Sally Boysen (video) Alex the parrot; Irene Pepperberg (video and comments by Euan MacPhail Psy 362S 2007, Lecture 9.1 slide 12
Chimpanzees greedy response The task: reward = amount not chosen Examples: 5 vs 2 objects -- chimps choose 5 numerals 5 vs 2 -- chimps choose 2 Experience with numerals does not improve performance with objects When objects are rocks, still choose more objects Psy 362S 2007, Lecture 9.1 slide 13 Monkeys and babies spontaneously count and add small quantities (video) The looking time test of counting and arithmetic Babies and monkeys look longer at impossible than at possible events Rhesus macaques on Cayo Santiago Island Susan Carey (author of the commentary reading) Psy 362S 2007, Lecture 9.1 slide 14 The magic show test of addition Habituate to simple displays e.g. 1 object screen 1 object 2 objects screen 2 objects Then show a test display 1+ 1 = 2 (possible outcome) or 1 + 1 = 1 (impossible outcome) Prediction: If subjects are adding, they will look longer at 1+1=1 than 1+1=2 Psy 362S 2007, Lecture 9.1 slide 15
Do babies and monkeys count and add? possible explanations Innate arithmetical ability? The same as used in later verbal counting and arithmetic. Perceptual object tracking? Not the same as true arithmetical ability Simple ability to track objects, available to non humans as well as humans Conclusions still controversial. More next Tuesday (NO CLASS on Thursday this week)