Falsification, Confirmation and Fallibility (cont.); Observation and categories

Transcription

1 Falsification, Confirmation and Fallibility (cont.); Observation and categories Phil 12: Logic and Decision Making Spring 2011 UC San Diego 4/12/2011

2 Announcements My office hours today only 1-2pm Remember to register iclickers - 2

3 Review: Falsification Argument form for falsifying hypotheses: If the hypothesis is true AND all auxiliary hypotheses needed to make the prediction are true AND the experimental setup is adequate, then the prediction will be true. The prediction is not true. Either the hypothesis is false, or an auxiliary hypothesis is false, or the experimental setup is not adequate. To the degree (and only to the degree) that we are sure that no auxiliary hypothesis is false and that the experimental setup is adequate, we can infer that the hypothesis is false.

4 The challenge of confirmation If the hypothesis is true, then the prediction is true. The prediction is true. The hypothesis is true. This is of the form affirming the consequent, and is invalid We can also see what is intuitively wrong with it Make up a theory (a really bad one) from which you predict that sunlight feels warm. Check the prediction. Sure enough, it is true That doesn t make your bad theory true 4

5 Confirming with unlikely predictions If the hypothesis were not true, then the prediction would not be true. The prediction is true. The hypothesis is true. This argument is valid, but is it sound? - - we have to be sure that the first premise is true Problem: typically there will be alternative hypotheses (major or slight variants of the one under consideration) that make the same prediction 5

6 Harvey s Alternative Hypothesis Rejecting Galen s hypothesis, Harvey proposed that: - - there is only one kind of blood this blood circulates out from the heart in the arteries and returns to the heart in the veins 6

7 How to secure positive evidence? Harvey could not see the connecting capillaries What kind of prediction could he make on the basis of his hypothesis that would be specific to it (i.e., not expected on other grounds)? - What would happen if Harvey is right and you permit blood to flow through arteries in your arm, but not through the veins? Harvey predicted and demonstrated swelling of the limbs 7

8 Harvey s circulation experiments 8

9 Harvey s circulation experiments If Harvey theory of circulation (i.e., that veins carry blood only toward the heart) weren t correct, you wouldn t expect the veins to remain emptied of blood. But veins do remain emptied of blood. Harvey s theory of circulation is correct. 9

10 Resistance and slow acceptance in the olden days patients were healed without the knowledge of the circulation, and that therefore, this doctrine, even if true, would be useless. (James Primrose, 1630) "If Harvey's idea of the circulation was correct, there would be many concoctions of the blood, an unlikely phenomenon, especially if one upheld the philosophical principal that in nature, simplicity and perfection remain inviolate." (Caspar Hofmann, 1636) Descartes (1637) accepted circulation, but proposed that heart was a furnace that heated the blood 10

11 Clicker question Are these figures the same or different? A. Same B. Different 11

12 Confirming a mental rotation hypothesis Hypothesis: People use mental images and operate on them in problem solving Prediction: If asked whether two rotated figures match, response times will vary with degree of rotation. If an image is not being rotated, reaction times should not correspond to degree of rotation. Reaction times do correspond to degree of rotation. An image is being rotated mentally. 12

13 Kosslyn on mental scanning Subjects memorize this map with landmarks such as a hut, a swamp, and a well. With the map gone, subjects were asked to: Imagine the map Focus on one object (e.g., the well), imagine a speck there Then move the speck in a straight line to a second object (e.g., the tree), and press button once there 13

14 Kosslyn on mental scanning ,.7 tu z 1.5 LU o: DISTANCE (cm.)

15 Kosslyn on mental scanning If subjects were not mentally scanning and moving the speck in their mental map, reaction times would not correspond to distances between objects. Reaction times do correspond to distances between objects. Subjects are mentally scanning and moving the speck in their mental map. 15

16 Bruner & Goodman (1947) Traditional view: perceiving is independent of one s beliefs and relies on what is there to be seen Bruner & Goodman s hypothesis: Perception is affected by one s beliefs Prediction: judgments of the size of a cardboard circle are quite accurate, but judgments of the size of a coin is affected by its value 16

17 Bruner & Goodman s results

18 Bruner & Goodman s results - 2 Rfch 10-yr. dds Poor lo-yr olds 18

19 Kosslyn on mental scanning If value did not influence perception, then there should be no overestimates of coin sizes. There are overestimates of coin sizes. Value does influence perception 19

20 Evaluating Hypotheses: The Simple and the Subtle In principle the logical evaluation of a hypothesis given evidence is simple: - If a hypothesis predicts something not otherwise expected, we tend to think it is true - If a hypothesis makes a false prediction, that counts against its truth But most interesting hypotheses in science both make new, unexpected predictions that turn out to be true and make predictions that turn out to be false No simple recipe for deciding whether to reject a hypothesis once it has made a false prediction or to hold onto it because of its record of true predictions 20

21 Fallibility Issues in science are seldom resolved by decisive experiments that once and for all falsify or confirm a hypothesis Hypotheses often take a long period to become established. And once established, a long period is often required to overthrow them All judgments in science are fallible subject to revision with more evidence 21

22 Observation

23 Preview: Observation At the foundations of science are procedures for gaining evidence about the world We learn about the world through our five senses, serve as our evidence - Tests of predictions ultimately rely on observation, both made with the unaided senses and with the use of instruments Before observations can be used for testing predictions, they must be brought under categories How reliable are observations? - Two fundamental questions about observation - What does categorization involve?

24 Clicker question Which Leaning Tower is more leaning? A. Left one B. Right one

25 Muller Lyer Illusion

26 Seeing more than one thing

27 Seeing what isn t possible: Escher

28 Seeing what isn t possible: Penrose Triangle

29 Seeing what isn t there

30 Ambiguities in real vision

31 Perception seems transparent But perception is underdetermined by sensory input (the information we receive via our sensory organs from the world) What we perceive depends on: - The way in which the visual system is constructed - The surrounding context - The effects of attention - What we have previously learned - What we expect to see How can we determine what is really out there?

32 Sensory Registration vs. Identification Vision (hearing, smelling, etc.) requires more than mere registration of stimuli on our senses It requires that we identify what we see, recognize an object as a tree, a street, or a car We typically only recognize those things with which we are already familiar, in contexts where they re expected - How, then, do we discover new things?

33 Clicker Recognizing question Do you recognize this? A. Yes B. No

34 Recognizing Familiar objects are often difficult to recognize when seen from an unusual perspective

35 The importance of context C T A T

36 Partial information We can also recognize things from partial information

37 Partial information We can also recognize things from partial information

38 Illusory contours

39 Clicker question How many letters f s (upper or lower case) are in the following sentence? Federal fuses are the result of years of scientific study combined with the first-hand experience of fifty years. A. 2 B. 4 C. 5 D. 8 E. 9

40 Federal fuses are the result of years of scientific study combined with the first-hand experience of fifty years.

41 Why proof reading is hard We see what we expect to see and so miss errors - This is exspecially truu when we have writen the text and now what is suposed to be their. To xllxstxatx, I cxn rxplxce xvexy txirx lextex of x sextexce xitx an x, anx yox stxll xan xanxge xo rxad xt wixh sxme xifxicxltx.