Week 4 — How Faint Can It Be? A Threshold Brief — Traditional alternative (no AI)
Instructors: publish this instead of the adaptive version if you prefer, and unpublish or delete the adaptive one.
Assignment 4 of the term — convert two classic threshold illustrations into new units, explain what an absolute threshold measures and why its conditions matter, and tell someone new to psychology how their eyes catch a faint light.
This week you learned to separate sensation from perception, to measure the edge of sensing with the absolute and difference thresholds, and to trace light to the rods and cones of the retina. In Week 2 you learned that a fuzzy idea becomes measurable only through an operational definition; the absolute threshold is that idea at work on the senses. In this assignment you work two short problems on classic illustrations, interpret each one, and explain to someone who has never studied psychology how their eyes catch a faint light. This week's lecture tutorial, quiz, discussion, and Analysis Workshop practise the same ideas from other angles.
The task
Galanter (1962) gave two classic illustrations of the absolute threshold, the weakest amount of a stimulus that a person can detect 50 percent of the time. On a clear, dark night, a person can detect a candle flame about 30 miles away. In a quiet room, a person can detect a clock ticking about 20 feet away. These are illustrations written with "about," not records from one experiment, and the conditions are part of each one.
Work these two problems, showing your arithmetic:
- Galanter (1962) illustrates the absolute threshold for hearing with a clock ticking about 20 feet away in a quiet room. There are 12 inches in a foot. About how many inches away is that clock?
- Galanter (1962) illustrates the absolute threshold for vision with a candle flame about 30 miles away on a clear, dark night. There are 5,280 feet in a mile. About how many feet away is that flame?
Beside each answer, add one brief interpretation of what the illustration measures and one limit of it. For problem 1, explain what "detected 50 percent of the time" means for the clock, why "in a quiet room" is part of the measurement, and what change to the ticking would count as a difference threshold instead. For problem 2, explain why "on a clear, dark night" is part of the measurement, say which receptors in the retina do most of the work for a faint light and why, and explain why the larger distance for the candle does not show that vision is "better" than hearing.
Show your arithmetic. A reader should be able to reproduce every number you report from the values above without guessing which values or steps you used.
Explain it to a non-expert
A friend who has never studied psychology is planning a night of stargazing. They plan to stare straight at the faintest stars and to check their brightly lit phone screen every few minutes. Write a 3–5 sentence message that explains, in everyday words, why a very faint star may be easier to catch slightly to one side of where you look, and why background light such as a bright screen can hide a faint light. Name one limit, such as how much thresholds differ from person to person. Explain any technical term in everyday words.
For a different, ungraded example, imagine a coffee-shop owner who asks why regular customers stop noticing the music after a while. Model answer: "Your music didn't get quieter; your regulars got used to it. When something stays the same, the senses slowly stop flagging it, so a steady playlist fades into the background. A new song or a change in volume brings it back to their attention. People differ, though, so a song one customer tunes out may still bother another."
Use that pattern for the stargazer, with your own explanation and evidence.
Deliverables
Submit a single threshold brief containing:
- the two answers, each with the arithmetic shown and a brief interpretation of what the illustration measures and one limit of it;
- your message to the stargazer, explaining in everyday words why a faint star may be easier to catch slightly to one side, why background light can hide a faint light, and one limit; and
- a one-line restatement of the values you used, so your results are reproducible.
Keep it to roughly one page. Clear and correct beats long.
Choose how you show it. Present your brief as written text, or as a recorded audio or video explanation of about three minutes with a transcript, or as a labelled sketch of the eye with a short note. Every form is graded by the same scoring criteria. Submit in any accessible file type or as a link; a recorded response may be submitted as audio or video with a transcript, or as text.
How you'll be graded
The full analytic rubric is attached to this assignment in Canvas.
Academic integrity and AI use
This version is designed to be completed without AI: do the computations, the interpretations, and the writing yourself, without a chatbot or other AI tool. You may use a calculator or a spreadsheet for the arithmetic. Submitting AI-generated work as your own, or copying another student's numbers, is an integrity violation under the course policy.
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