Experimental Design. Jeff Wickens Neurobiology Research Unit

Transcription

1 Experimental Design Jeff Wickens Neurobiology Research Unit

2 Outline Define experimental design Develop an experimental question and hypothesis Non-declarative learning Activity-dependent synaptic plasticity Adaptation to sensory transformations Create an experimental design Prism shift procedures Research question Conduct your experiment

3 Good experimental design Experimental design is the part of statistics you do BEFORE you start an experiment. Allows causal inferences (independent and dependent variables) Reduces confounding effects of extraneous variables Reduces variability within treatment conditions

4 What is experimental design? An experimental design is a plan for assigning experimental units to treatment conditions. History of experimental design James Lind (Scurvy) Ronald Fisher (Agriculture) Clinical Trials (Medicine) Placebos introduced George Box (Chemistry) Finance and Service industries Basic science research in psychophysics, biology, psychology, chemistry

5 Example experimental designs Divide participants into two groups, experimental group and the control, Introduce a change to the experimental group and not the control group.

6 Independent measures Use separate groups for each treatment Independent variable = number of throws Group A (10 subjects) Group B (10 subjects) Group C (10 subjects) Dependent variable = some measure of learning or after-effect Prone to confounding effects of extraneous variables: randomization may be required

7 Repeated measures Same participants take part in each treatment Independent variable = number of throws Group A (10 subjects trial 1) Group B (10 subjects trial 2) Group C (10 subjects trial 3) Dependent variable = some measure of learning or after-effect Counterbalancing (ABC BCA CAB) may be needed if order effects

8 Matched groups Participants matched for some characteristic (age, IQ, baseline performance, fitness etc) Independent variable = number of throws Group A (10 subjects) Group B (10 subjects) Group C (10 subjects) Dependent variable = some measure of learning or after-effect Identical twins / triplets etc would be ideal

9 Outline Define experimental design Develop an experimental question and hypothesis Non-declarative learning Activity-dependent synaptic plasticity Adaptation to sensory transformations Create an experimental design Prism shift procedures Research question Conduct your experiment

10 HM: learning about memory from a patient with amnesia Corkin et al H.M.'s medial temporal lobe lesion: findings from magnetic resonance imaging. J Neurosci 17:

11 H.M. s Memory Unable to store new memories of facts and events Does not recognize people, place he lives, himself Does not remember what he ate for breakfast Does not remember world news but retains learning ability Milner B Amnesia following operation on the temporal lobes. In: CWM Whitty and OL Zangwill (eds). Amnesia, pp London: Butterworths.

12 Multiple types of memory depend on different brain areas (Semantic) (Episodic)

13 Pyramidal cells of the cerebral cortex Braitenberg and Schüz (1991)Anatomy of the Cortex: Statistics and Geometry. Fig 75

14 Connections of pyramidal cells Braitenberg and Schüz (1991)

15 What is the physical basis of memory? Hebb (1949) proposed when an axon of a cell A persistently and repeatedly takes part in firing a cell B, some growth or metabolic change takes place such that A s effectiveness in firing B is increased. A B

16 Hebb also proposed that things are represented in the brain as cell assemblies

17 Hebbian rule makes cell assemblies

18 Remembering by cell assembly ignition

19 Remembering by cell assembly ignition

20 Is Hebb s rule true? An experimental test Bliss and Lomo, 1973

21 Activity dependent plasticity (long-term potentiation, LTP) demonstrated in brain slice Bliss and Lomo, 1973

22 Summary There are multiple types of memory and learning The brain shows activity-dependent plasticity Activity-dependent plasticity is a possible mechanism for memory and learning

23 Outline Define experimental design Develop an experimental question and hypothesis Non-declarative learning Activity-dependent synaptic plasticity Adaptation to sensory transformations Create an experimental design Prism shift procedures Research question Conduct your experiment

24 Research Question What is the effect of active movement on plasticity?

25 Adjustment to transformations of vision 19 th Century investigator, Hermann von Helmholtz brain adjusts to transformations of vision More than a change in sensory processing muscles and motor system involved too correlation of active movement and sensory consequences important

26 Research Question What is the effect of active movement on plasticity? Operational definition of active movement and plasticity Measure prism adaptation and after-effect. Compare the effects of passive perception and active movements on adaptation.

27 Prism Adaptation From: Martin et al. (1996) Throwing while looking through prisms. I. Focal olivocerebellar lesions impair adaptation. Brain 119, , Figure 1.

28 Measures of performance and adaptation Performance: standard deviation of horizontal errors (last 8 throws) Adaptation: rate constant of exponential decay function, location versus trial number y = a b Exp[-t/c] a is asymptote b is magnitude c is rate constant

29 Independent variables (treatments, factors) different training conditions Active movement during prism shift Passive perception during prism shift Pointing during prism shift (your ideas)

30 Effect of number of training throws Fernandez-Ruiz J, Diaz R (1999). Prism adaptation and aftereffect: specifying the properties of a procedural memory system. Learn Mem 6(1):

31 Effect of degree of displacement Fernandez-Ruiz J, Diaz R (1999). Prism adaptation and aftereffect: specifying the properties of a procedural memory system. Learn Mem 6(1):

32 Your task Design an experiment to test the hypothesis that active movement and its sensory consequences are necessary for adaptation Start with defining dependent variables, independent variables Assign subjects to treatments Think about how to analyze your data

33 Outline Define experimental design Develop an experimental question and hypothesis Non-declarative learning Activity-dependent synaptic plasticity Adaptation to sensory transformations Create an experimental design Prism shift procedures Research question Conduct your experiment

34 Have fun!

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36 Prism adaptation causes changes in brain activity in selective regions Seidler et al. (2006) Exp Brain Res 175:

37 Original Patient s copy Left unilateral neglect caused by damage to the parietal cortex of the right hemisphere of the brain The Stanford Encyclopedia of Philosophy 2014

38 Prism adaptation rehabilitates neglect Rossetti et al (1998) Nature 395,

39 Thanks