Problem Set 2

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Apr 3, 2024

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ISE 3614: Introduction to Human Factors Engineering Problem Set 2 Instructor: Nathan Lau, PhD The problem set is worth 2.5% of course grade. Please read all the instructions carefully. Do NOT show or present answers to your classmates or anyone! You are allowed to consult any course materials. Write your answers on the Problem Set directly. Read each question carefully. You have to submit this problem set on CANVAS on Midnight of Feb 27 th (Thursday). GOOD LUCK! Notes: ● I will not struggle to read illegible writing so write clearly. If I can’t read it, it is wrong. ● I will only grade the first answers I come across (e.g. if I ask for 2 and you give 3, I will only grade the first 2 regardless of what is listed third). Therefore, think about what you want your answer to be or which question you want to answer and don’t waste time or room on answers that won’t be graded. ● In addition, remember to provide specific answers/responses to each question. Student Name: ______ Jenna Cameron ____________ Student ID: _________ 906538402 ____________ Honor Code: If you have followed the Honor Code, you should sign the following pledge after you finish this problem set. (We are not required to grade the assignments in which the Honor Pledge has not been signed.) "I have neither given nor received unauthorized assistance on this assignment." Signature: ______________________________

ISE 3614 – Human Factors and Ergonomics Spring 2024 Practice Exercise 2. Auditory Systems & Signal Detection Part 1: Auditory Systems & Noise 1. What is the total sound pressure level in lane stadium of music playing at 95dBA, fans cheering at 100dBA, and the announcer talking at 90dBA? Please show all work and specify the units as appropriate. L ∑ ¿ = 10 log 10 ( 10 L 1 10 + 10 L 2 10 + 10 L 3 10 ) ¿ L 1 = 95 dBA ,L 2 = 100 dBA ,L 3 = 90 dBA L ∑ ¿ = 10 log 10 ( 10 95 10 + 10 100 10 + 10 90 10 ) = 10 log 10 ( 10 9.5 + 10 10 + 10 9 ) = 10 log 10 ( 11063127227.77 ) = 101.51 dBA ¿ 2. A construction worker must operate a jackhammer, which generate 105dBA of noise, and drive a construction vehicle, which generate 80dBA of noise, for cement paving. Every hour of jackhammer operation only needs half an hour of construction vehicle use. Without hearing protection, how much time should the worker operate the jackhammer and construction vehicle a day according to the OSHA 1983 standard. Be sure to show all work. Please specify the units as appropriate. D = 100 × ∑ n = 1 N C n T n 105dBA permissible time = 1 hour 80dBA permissible time = 32 hours x 1 + .5 x 32 = 1 → 32 x 32 + .5 x 32 = 32 32 → 32.5 x = 32 → x = 0.9846 hours 0.9846 2 = 0.492 0.9846 hours of jackhammer and 0.4923 hours of cement paving. 3. The Hokie Bird mascot has been complaining of ringing in his ears and hearing loss after the Virginia Tech vs. Purdue football game. As part of his on-field duties at the football game, the Hokie Bird was exposed to 90dBA for 4 hours, and 95dBA for 1 hour, 100

dBA for 2.5 hours, and 105dBA for 0.5 hours. Is this safe? Calculate the Time Weighted Average Exposure for the Hokie Bird. TWA = 90 + 5 log 10 ( 2 ) × log 10 ( D 100 ) , D = 100 × ∑ n = 1 N C n T n , C n = hours worked, T n = permissible work hours D = 100 × ( 4 8 + 1 4 + 2.5 2 + 0.5 1 ) = 250% TWA = 90 + 5 log 10 ( 2 ) × log 10 ( 250 100 ) = 96.6 dBA The TWA is 96.6 dBA for this 8-hour shift for the Hokie Bird. According to the table in the appendix, the acceptable sound level for 8 hours is 90 dBA. Since the Hokie Bird was exposed to a sound level greater than that, this environment was not entirely safe for the Hokie Bird. Part 2: Signal Detection 4. Solve the following Signal Detection Theory problems. The probabilities in the table below represent the likelihood of each response made by an individual while undergoing a hearing test with noise-canceling headphones. These responses indicate the perception of hearing a faint sound amidst background noise in a testing environment. Use the z- table from appendix. RESPONSE YES NO SIGNAL YES Hit: 0.85 Miss: 0.15 NO False Alarm: 0.01 Correct Rejection: 0.99 (1) What is the nearest value to the Hit probability on the z table?

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0.8508 (2) What is the z-value of the Hit probability? 1.04 (3) What is the nearest value to the False Alarm probability on the z table? 0.0099 (4) What is the z-value of the False Alarm probability? -2.33 (5) What is the equation to get Estimate d´? (substitute the values you obtained from (2) and (4) into the equation (1)) Estimated d ' = ( 1.04 ) − ( − 2.33 ) = 3.37 (6) What is Estimate C? Estimated C =− 0.5 ( 1.04 + ( − 2.33 ) ) = 0.645 (7) If d´ > 2, that pilot is good (sensitive). Based on this cut-off, is this pilot good? Circle one of the two. Good vs. Not good (8) Is this pilot liberal or conservative in terms of enemy detection? Liberal 5. A participant is asked to listen to a series of (120) tones played through headphones and determine whether each tone is high-pitched (non-target ) or low-pitched (target ). The participant responds “high” when he believes the tone is high-pitched and “low” when they believe it is low-pitched. 10 low-pitched tones were hidden among the 120 tones that the individual had to examine. The results showed that the inspector reported 15 low-pitched tones, while the supervisor confirmed 8 were correct. Please answer the following questions based on the signal detection theory. a) Please identify the number of signals and noise for this inspector’s job 120 tones 10 low pitched tones / 110 high pitched tones

b) Create the 2x2 stimulus-response matrix that shows the numbers of hits, misses, false alarms, and correct rejection RESPONSE Signal Present 10 Signal Absent 110 SIGNAL YES (15) Hit: 8/10 Miss: 7/110 NO (105) False Alarm: 2/10 Correct Rejection: 103/110 6. Two inspectors were compared under similar conditions at removing defective parts from the assembly line. Their performance was measured as follows: Inspector A: Hit rate of 0.81 and false alarm rate of 0.21 Inspector B: Hit rate of 0.84 and false alarm rate of 0.44 a) Which would you choose if the cost of releasing a defect was very high? why? I would choose Inspector A because he has a lower false alarm rate, meaning he is more cautious. b) Which inspector does a better overall job (hint: consider d') d ' = Z ( H ) − Z ( FA ) d A ' = 0.808 − ( − 0.801 ) = 1.609 d B ' = 1.00 −(− 0.15 )= 1.15 Since the d’ value for Inspector A is greater than the value for Inspector B and closer to 2 than Inspector B, Inspector A does a better overall job.

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