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日期:2019-12-03 10:03

Due: 26 November 2019 PLID50 | Lab 4/5

Lab 4/5: Top-down effects on Perception

These final two laboratory assignments examine a very similar phenomenon: how other cues

(e.g., faces, words) affect your perception of speech sounds. Here, you will synthesize the skills

you have acquired in the course to this point – data summarization, plotting, outlier rejection,

reasoning about results. Assignments that are explanatory and well-written will receive higher

marks. The writing will be coherent and demonstrate thought about the purpose of the assignment

and the potential research question tackled by the lab. Each lab will be worth 50 points.

This will result in 100 points total. Please turn in one PDF file to Quercus by November 26.

Lab 4

Methods Lab 4 was a phoneme identification experiment. Your task was to determine if you

heard [sɑ] or [?ɑ]. Sounds were paired with faces that appeared on the screen. A nine-step [s]-

[?] continuum was constructed from a female voice who produces the sounds naturally. The continuum

was created by gradually cross-mixing the two sounds together such that at one point on

the continuum, the sound was 100% [s]/0% [?] (s1) and at the other end of the continuum, the

sound was 0% [s]/100% [?] (s9). The midpoint (s5) was 50% [s]/50% [?]. Using the Change

Gender function in Praat (Boersma & Weenik 2001), we adjusted the median pitch of each token

to 140 Hz and adjusted the Formant Shift Ratio by a factor of 0.7. This was done to construct

tokens that were relatively ambiguous with respect to the gender of the talker. Each of the

nine tokens were paired with two faces: a male caucasian face and a female caucasian face.

This led to a 2 x 9 design: Condition (male vs female) x Continuum (nine steps). The ITI was

1000 ms. The face and sound file were played simultaneously. The face remained on the

screen for 1000 ms or until a response was made and the next trial began. Ten repetitions per

stimulus/face combination were played, resulting in 180 total trials (18 combinations (2x9) presented

10 times each). The experiment took approximately 5 minutes to complete. Eleven students

participated. Participants were instructed to press the ’s’ key if they heard [sɑ] or the ‘h’

key if they heard [?ɑ]. Reaction times were calculated at the onset of the syllable presentation.

1. Methods: Provide a brief synopsis in your own words about the goal of the study (you might

have to write this after you analyze the data) and the methods employed. Minimally, state

the task, design, stimuli, number of participants and number of trials. This information is provided

above, but write it in your own words. Do not copy and paste what I have provided.

2. Outlier rejection: Provide a by-participant histogram for the reaction times for each participant

(you should have a total of 20 histograms). Identify a reasonable outlier rejection criterion.

State this. Apply this rejection method and re-plot the by-participant RT histograms. You

should present two plots (1 before and 1 after outlier rejection and the criterion that was

used).

3. Plot: Provide a geom_line() + geom_point() + geom_errorbar() ggpplot of the proportion [s]-

responses on the y-axis and continuum on the x-axis. You should be plotting your cleaned

data here. Note that you may have to create a new column that numerically codes for

whether the participant responded “s” or “sh”. Your plot should contain error bars of the

standard error of the mean. Moreover, the axes should be labeled coherently and not using

the default labels.

4. Interpret: Is a perceptual bias present in the results? That is, does the presentation of a face

in conjunction with a speech sound change our perception of the speech sound. Be specific.

Where is this bias present? How do we conclude, specifically, from the results that this bias

exists?

Due: 26 November 2019 PLID50 | Lab 4/5

5. Compare: Consult Strand & Johnson (1996) Experiment 3, where visually presented faces

were played in conjunction with the speech sounds. In particular, focus on Figure 2.3. Compare

the results in Q3 here to their Figure 2.3. What are the similarities and differences?

Note that I am not interested in the particulars of the plot (e.g., they used percentages, s1

was most [?] like). Focus on the qualitative pattern of data.

6. Statistics: Finally. identify the ambiguous point in the plot and run a t-test (though note that

we are ignoring the assumptions of the test for the purposes of this assignment). State your

findings in paragraph form, include your null and alternative hypotheses, and conclude

whether or not we can accept or reject the null hypothesis, i.e., no effect of gender of face

on perception of speech sounds. Remember that p < 0.05 is our criterion for rejecting the

null hypothesis.

Lab 5

Methods Lab 5 was also a phoneme identification experiment. In particular, you heard a CV(C)

(C) syllable and were asked to respond whether the initial consonant was [k] or [g]. A seven step

continuum was constructed by manipulating the duration of VOT: 11 ms, 18 ms, 25 ms, 33 ms,

40 ms, 47 ms, and 54 ms in duration. Recall that VOT is primary acoustic cue for voiced versus

voiceless stop/plosive consonants in English. These seven tokens were embedded inside of

three _V(C)(C) frames: [_?], [_?ft] and [_?s]. The ITI was 1000 ms. The next trial began after a

response via button press: ‘k’ if they heard the [k] sound and ‘g’ if they heard the [g] sound . The

experiment design was 3 x 7 (Frame (3 frames) x Continuum (7 steps)). This led to 21 total

combinations. Each stimulus was played 12 times, resulting in 252 total trials per participant. A

total of 14 students participated in the experiment. Each experimental session lasted approximately

15 minutes.

7. Methods: Provide a brief synopsis in your own words about the goal of the study (you might

have to write this after you analyze the data) and the methods employed. Minimally, state

the task, design, stimuli, number of participants and number of trials. This information is provided

above, but write it in your own words. Do not copy and paste what I have provided.

8. Outlier rejection: Provide a by-participant histogram for the reaction times for each participant

(you should have a total of 14 histograms). Identify a reasonable outlier rejection criterion

(e.g., > 5 sec). Apply this rejection and re-plot the by-participant RT histograms. You

should present two plots (1 before and 1 after outlier rejection and the criterion that was

used).

9. Plot: Provide a plot of the proportion [g]-responses on the y-axis and continuum on the xaxis.

This should be one geom_line + geom_point() ggplot with three distinct lines, one for

each Condition/Word Frame. These should be colour coded.

10. Interpret: Does the presentation of a _V(C)(C) frame in conjunction with a speech sound

change our perception of the speech sound? Be specific. Where is this bias present? How

do we conclude, specifically, from the results that this bias exists?

11. Extend: What does this perceptual bias mean? It is important to consider the relationship

between the interpretation of the speech sound and its phonetic frame. What is the information

that is causing the observed perceptual bias? Is there a control in the experiment? If so,

what do you consider to be the experimental control?

12. Compare: Consult Ganong (1980) Experiment 1, where visually presented faces were

played in conjunction with the speech sounds. In particular, focus on Figure 3. Compare the

results in Q9 here to his Figure 3. What are the similarities and differences? Note that I am

not interested in the particulars of the plot. Focus on the qualitative pattern of data.


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