Psychology 360 January 30, Lateralization lab

Transcription

1 Psychology 360 January 30, 2006 Lateralization lab Today we ll conduct two (not one, but two!) experiments that should show us some interesting things about brain lateralization and the overall structure of the nervous system. In particular, we ll consider the unique contributions of the left and right hemispheres, and what happens as information is transferred from one hemisphere to the other. I should point out that there s no need to conduct these two experiments in any particular order. Experiment #1 is simply labeled as such for the sake of convenience and could just as easily be conducted second (in fact some of you will probably want to do so, in order to decrease competition with other groups for equipment). So, split into groups of 2 or 3, and gather the appropriate materials for one of the two experiments. When you re finished, return the materials to room 317 and gather the materials necessary to complete the other experiment. When you re finished with both experiments, check to see that your data have been recorded accurately, and leave the data sheets with me. I ll compile results to show you at a later time. Once you ve turned in your data, start to consider the analysis questions. Responses to these will be due by our next lab meeting (Monday, February 6 th ).

2 Experiment #1: Tactile letter identification Read through the entire methodology before beginning. Then each person in your group should take turns serving as a participant and as an experimenter. Be sure to carefully record your data on the data sheet provided. Materials: For this experiment, you ll need a digital stopwatch, a box of children s toy magnetic letters, and a blindfold. Place the blindfold so that the participant cannot see. It should be snug but not so tight as to produce any physical discomfort. If you re having trouble with this, you can simply have the participant close their eyes or avert their gaze. It s really not that difficult. Practice trials: On each trial, the experimenter should blindly draw a letter from the box and place it into the hand of the participant, face up (colored side up). As soon as the letter is in the hand of the participant, the experimenter should begin timing with the stopwatch while the participant tries to verbally identify the letter as quickly as possible. Participants may move, touch, and otherwise manipulate the object, but only with the hand into which the letter was placed. When the participant correctly identifies the letter, the experimenter should stop the watch and note the latency of the correct response. If the participant incorrectly identifies the letter, the experimenter should simply say incorrect and continue timing until a correct response is given. Participants should complete 2 practice trials with each hand and be comfortable with the procedure before moving on to the test trials. Practice trial data need not be recorded. Test trials: Conduct 20 letter identification trials (each time with a new letter), alternating hands on each trial. This will result in 10 trials using the right hand and 10 trials using the left hand. The experimenter should take care to avoid selecting ambiguous letters (for instance, lower case p and d are identical save for the rotation, and should be avoided). Using the same letter for multiple trials is acceptable, if a letter is randomly selected again. The number of errors made before a correct identification should be recorded on the data sheet along with the response time (to the nearest second) after each trial. Data summary: After having completed all 20 trials, determine the median response time for letter identification with the left hand, and the median response time for letter identification with the right hand. The median is the middle score when scores are arranged from lowest to highest. For example, the median of the data set (5, 8, 8, 12, 15) would be 8. If there is an even number of scores, the median is half way between the two middle scores. Thus, the median for the data set (5, 8, 8, 12, 15, 16) would be 10 (half way between 8 and 12).

3 Experiment #2: Verbal interference with a manual task. Read through the entire methodology before beginning. Then each person in your group should take turns serving as a participant and as an experimenter. Be sure to carefully record your data on the data sheet provided. Materials: For this experiment, you ll need a digital stopwatch and a wooden dowel 92 cm in length. Be careful with the wooden dowels, as they are potentially hazardous to eyes and other soft tissue. Practice trials: For each trial, the participant should position one end of the wooden dowel on their index finger, so that the dowel extends straight toward the ceiling, and attempt to balance it, unsupported, as long as possible. Participants may move about freely in attempts to maintain balance (stepping, walking, stretching, etc. are all acceptable). The experimenter should start timing with the stopwatch when the participant begins balancing the dowel, and stop as soon as the dowel falls, contacts a wall, or the participant touches it with any part of the body other than the index finger. Obviously, you ll want to find a space where you have some room to move about. Participants should complete 5 practice trials with each hand and be comfortable with the procedure before moving on to the test trials. Practice trial data need not be recorded. Test trials: Conduct 20 dowel balancing trials: 10 with the left hand, and 10 with the right. Half of these trials (5 of the left-hand trials, and 5 of the right-hand trials) should be conducted in silence, exactly as outlined above. On the remaining trials, the participant will complete a verbal task while balancing the dowel. The experimenter will read a word from the list on the next page, and the participant should spell the word backwards. Once a word has been spelled backwards, the experimenter should prompt the participant with a new word, and continue to do so until the end of the trial (ie, until the dowel is dropped). Conduct 20 trials, in the order indicated on the data sheet. After each trial, the experimenter should record the total balancing time, to the nearest second. Some people can balance dowels for a long time, so you may go through several words per trial. If you reach the end of the list, simply start over at the beginning. Data Summary: Compute a median response time for each of the 4 kinds of trials (right hand without spelling, right hand with spelling, left hand without spelling, and left hand with spelling) and write them on your data sheet. Instructions for calculating a median can be found in the data summary section of Experiment 1.

4 Word list for the backward spelling task. Soap Bone Yarn Towel Flower Money Tongue Snow Pen Glue Key Beach Fire Needle Puddle Cloud Cotton Cradle Joke Zebra Clock Mechanic Knife Rock Shield Tornado Elastic Car Pan Apple Stork Oar Tree Ruler Election Dog Cockroach Cave Lion Volcano Storm Head Keyboard Paperclip Stylus Spindle Board Cycle Collar Heart Chip Spice Stable Antique Vest Stereo Rifle Athlete Magic Ceiling Chain Creature Violin Stump Delivery Salmon Energy Rocket Flurry Quarter Hotel Parrot Incident Note Joust Mirror Kite Lounge Spoon Sticker Noise Water Animal Brain Number Sugar Horse Sweater

5 Psychology 360 Spring, 2006 Experiment 1 Data Sheet Trial # Hand Letter identified Errors Response latency 1 Right 2 Left 3 Right 4 Left 5 Right 6 Left 7 Right 8 Left 9 Right 10 Left 11 Right 12 Left 13 Right 14 Left 15 Right 16 Left 17 Right 18 Left 19 Right 20 Left Participant s handedness (circle one): Right Left Median response time for left-hand trials: Median Response time for right-hand trials:

6 Psychology 360 Spring, 2006 Experiment 2 Data Sheet Trial # Hand Verbal task Total balancing time 1 Right No 2 Right Yes 3 Left No 4 Left Yes 5 Right No 6 Right Yes 7 Left No 8 Left Yes 9 Right No 10 Right Yes 11 Left No 12 Left Yes 13 Right No 14 Right Yes 15 Left No 16 Left Yes 17 Right No 18 Right Yes 19 Left No 20 Left Yes Participant s handedness (circle one): Right Left Median response times for right-hand trials without backward spelling: Median response times for right-hand trials with backward spelling: Median response times for left-hand trials without backward spelling: Median response times for left-hand trials with backward spelling:

7 Psychology 360 Spring, 2006 Letter Identification Experiment Analysis Questions Due Monday, February 6 th 1. Which brain area (hemisphere and lobe) initially processes the somatosensory input on left-handed letter identification trials? 2. Which brain area initially processes the somatosensory input on right-handed letter identification trials? 3. In most right-handed individuals, which hemisphere actually identifies the letter and produces the verbal response? 4. Compare your responses to questions 1-3. Which condition would you expect people will be better at (ie, achieve greater accuracy and faster response times)? Explain your prediction. 5. How would the results be different if I had secretly severed all of your corpus callossa? Can you be reasonably certain that you remain neurologically intact? Explain why.

8 Balancing Experiment 1. Which brain area (hemisphere and lobe) was primarily in control of balancing the dowel on left-handed trials? 2. Which brain area was primarily in control of balancing the dowel on right-handed trials? 3. Which brain area (hemisphere and lobe) would be used for the backward spelling task in most right-handed people? 4. Compare your answers to questions 1-3. What should happen in left- and righthanded trials as the backward spelling task is introduced? Justify your answer. 5. How would the answer to the previous question be different in the minority of people whose language functions are lateralized in the right hemisphere? 6. Do these results suggest that your language functions are in your right hemisphere or your left hemisphere? Is this the same conclusion you came to from our in-class experiment (in which words were quickly flashed to the left and right of a fixation point)?