Instructions

This assignment assesses your understanding of key components of the perception section of the course. You are required to attempt all of the questions that are specified in this document.

Please complete your responses within the template document, which can be downloaded from the course Moodle site. There are otherwise no specific formatting requirements for your responses.

Drawing

Question 3 requires submission of a drawing or illustration. You are free to complete this however you prefer—hand-drawn and scanned or computer-drawn are both acceptable. As long as the information in your drawing is communicated properly, there is no association between marks and the “quality” of illustration.

Additional Readings

All questions can be answered on the basis of information from lectures and tutorials. There is no requirement or expectation for additional reading. Should you desire to reference any additional material, APA format is appropriate.

Marking Criteria

Each of the four questions are worth 25 marks in total, for an overall total of 100 marks for the assignment. Each question has multiple components, with each component contributing a specified number of marks.

Submission

Your completed assignment is to be submitted online via the Moodle course site. The relevant link is “Perception assignment”, which is found in the “Perception Assignment” section. You are not required to submit a hard copy to the School of Psychology office.

The formatting of submitted documents may be altered when viewed within the Moodle system. Your formatting is likely to be better preserved if you submit your document as a PDF (exported from Word) rather than as a Word document. If you notice that the formatting of your submission is altered in a way that may affect legibility or interpretability, please email your tutor as soon as possible.

Due Date

The assignment is due by 11:55pm Friday 1st September. Late submissions will be allowed but a penalty rate of 2% per day it is late will be applied.  All late submissions must be received by 15th September.

Extensions

Unless there are valid and substantial medical or other circumstances, no extensions for this assignment will be granted. Applications for extensions must be submitted using the MyUNSW Special Consideration system.

Question 1 overleaf

Question 1 (25 marks)

Imagine that you are designing an experiment that has the aim of determining the minimum intensity of light that is reliably detectable by human observers. That is, you would like to know how dim you could make a flash of light and still have it be reliably seen.

• 1. In designing the experiment, you need to make some decisions in order to optimise the ability of the observers to detect the flash. Based on the descriptions of visual processing given in lectures and tutorials, for each of the following state which option you would select and explain your decision (4 marks each; 1 mark for selection, 3 marks for explanation). Remember, the goal is to optimise the observer’s ability to detect the flash.
  • 1a. Prior to beginning the experiment, your observer will sit for 30 minutes in either a well-lit or a dark room (4 marks).
  • 1b. You will present the flash to either the observer’s fovea or periphery (4 marks).
  • 1c. The flash will have a monochromatic spectral distribution at 450nm, 500nm, or 550nm (4 marks).
  • 1d. The flash will be shown for 0.1 seconds or for 1 second (4 marks).
• 2. Suppose that you intend for the observers to perform a series of trials, where each trial consists of a flash of light being shown and then the observer is asked to respond whether they saw it or not.
  • 2a. Describe why this approach may not allow you to accurately measure the sensitivity of an observer (4 marks).
  • 2b. Describe how you could change the experiment to reduce this problem (5 marks).

Question 2 overleaf

Question 2 (25 marks)

This question assesses your understanding of the relationship between the physical stimulus and its real-world properties.

• 1. When viewing the scene depicted below (left), people typically perceive the upper square region of the central object as being darker than the lower square region of the object. This is despite the two squares being identical in luminance, as demonstrated by presenting the square regions in isolation (below right). With reference to the scene depicted below (left) (8 marks):
  • 1a. If both the upper and lower surfaces had 100% reflectance, the luminance would be greater in the upper square region compared to the lower square region. Use this additional information to compare the illumination of the upper and lower square regions (2 marks).
  • 1b. Describe how illumination, luminance, and reflectance are related, and use this relationship to compare the reflectances of the upper and lower square regions (6 marks).

Question 2 continues overleaf

• 2. In the scene depicted below (left), the upper person is typically perceived as being physically taller than the lower person. This is despite the two people being identical in retinal size (horizontal extent), as shown when presented in isolation on the right in the image below. With reference to the scene depicted below (left) (8 marks):
  • 2a. If both the upper and lower people were of equal physical size (equally tall), the retinal size of the upper person would be smaller compared to the lower person. Use this additional information to compare the distance of the upper and lower people (2 marks).
  • 2b. Describe how distance, physical size, and retinal size are related, and use this relationship to compare the physical sizes of the upper and lower people (6 marks).

• 3. There is an analogous relationship between the scenarios in Questions 2.1 and 2.2. Identify this analogy by matching the terms used in Question 2.1 (listed alphabetically: illumination, luminance, and reflectance) with the corresponding term used in Question 2.2 (listed alphabetically: distance, physical size, retinal size), and explain your reasoning for the matches that you make between the terms (9 marks).

Question 3 overleaf

Question 3 (25 marks)

This question assesses your understanding of monocular cues to depth.

Imagine that you are standing on a soccer field. There are three soccer balls on the field, each like the depiction below. The three soccer balls are at different distances from you, but are the same physical size.

• 1. Produce an illustration in which you use at least three of the following monocular cues to convey the depth relationship among the three soccer balls. That is, draw a picture that depicts, from your vantage point in the scene described above, that the soccer balls are at different distances (2 marks per cue, 6 marks total).
  •  Occlusion
  •  Retinal size
  •  Retinal position
  •  Aerial perspective
  •  Linear perspective
• 2. Explain how each of the three cues that you chose from the list above conveys that the soccer balls are at different distances in your drawing (3 marks per cue, 9 marks total).
• 3. Imagine that there is a soccer ball, a tennis ball, and a golf ball (instead of the three soccer balls) and that you are trying to determine the relative depth relationships among the three balls.
  • 3a. Explain why the retinal size of the balls is an ambiguous cue to depth if you, as the observer, cannot make any assumptions about the physical size of the balls (4 marks).
  • 3b. Explain how having the three different types of ball affects your use of relative and familiar size information to disambiguate the retinal size cue to depth (3 marks each).

Question 4 overleaf

Question 4 (25 marks)

This question assesses your understanding of the processes and challenges involved in sensing visual motion.

Consider the stimulus that is depicted in the following space-time representation, where horizontal space goes from left to right with increasing pixels and where the overlaid rectangles indicate the spatial receptive field locations of two “intensity neurons”:

• 1. Identify which of the following descriptions best matches the physical stimulus that is depicted in the space-time diagram, and explain your decision (3 marks):
  •  “A set of four horizontally-spaced dots moves to the left”
  •  “A set of four horizontally-spaced dots moves to the right”
  •  “A set of four horizontally-spaced dots moves down and to the left”
  •  “A set of four horizontally-spaced dots moves down and to the right”
• 2. You are seeking to create two neural motion detection circuits of the kind that we have discussed in lectures and tutorials; one for ‘leftwards motion’ and one for ‘rightwards motion’. Explain which of the two “intensity neurons” would be connected to a “delay neuron” for each of these two neural motion detection circuits (5 marks).
• 3. Describe the role of the “comparator neuron” in a neural motion detection circuit (5 marks).
• 4. Imagine that you have created a large set of separate neural motion detection circuits (100, for example) that each start with the two “intensity neurons” depicted in the space-time diagram. The “delay neuron” is connected to the left “intensity neuron” in 50 of the circuits, and each of these 50 circuits has a different delay time, ranging from very short delays (< 0.5 seconds) to longer delays (> 1.5 seconds). The other 50 circuits have the same range of delay times, but the “delay neuron” is connected to the right “intensity neuron”. Explain why it is difficult to establish the speed (6 marks) and direction (6 marks) of the physical stimulus that is shown in the space-time diagram from the output of this set of circuits (12 marks).