Teachers notes

Professor Ross Day



Summary of career
Extract from interview and focus questions

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Professor Ross Day was interviewed in 2011 for the Interviews with Australian scientists series. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge and view science as a human endeavour. These interviews specifically tie into the Australian Curriculum sub-strand ‘Nature and development of science’.

The following summary of Professor Day’s career sets the context for the extract chosen for these teachers’ notes. The extract discusses three different visual illusions that Professor Day researched. Use the focus questions that accompany the extract to promote discussion among your students.

Summary of career

Ross Henry Day was born in Albany, WA in 1927. Day completed his secondary education at Albany High School in 1945 and then started a BSc (Hons) at the University of Western Australia (1946-49). While in his third year, Ross Day was offered a graduate assistant position in psychology, which he held throughout his honours year. In 1950 Day moved to the University of Bristol, first as an assistant lecturer (1950-51) and then research fellow (1951-55). Whilst at the University of Bristol, Ross Day completed a PhD in psychology (1952-54). His PhD work was on perceptual factors in the control of high performance aircraft.

Dr Day returned to Australia and the University of Sydney as lecturer (1955-59), then senior lecturer (1959-61) and finally reader (1962-64). During this period at Sydney University, Dr Day carried out research into motion after effects and spent a year on sabbatical at Brown University on Rhode Island, USA (1961). Monash University then offered Dr Day the foundation chair of the department of psychology, which he accepted. Professor Day was at Monash from 1965 to 1992 and, as well as establishing a strong experimental psychology department, he served as associate dean of the faculty of science from 1981-83. While at Monash, Professor Day wrote a book called Human Perception and continued to study visual illusions such as the Ames room. After retirement Professor Day became adjunct professor in psychology at La Trobe University where he continues to conduct experiments into perceptual illusions.

Professor Ross Day received an honorary doctorate from La Trobe University in 1988 and has been honoured by fellowships to several prestigious societies and academies including; foundation fellow of the Australian Psychological Society (1964), fellow of the Academy of Social Sciences in Australia (1967) and fellow of the Australian Academy of Science (1990).

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Extract from interview

Motion After-Effect, Ames Room and the Müller-Lyer Illusion

When you think back about the research that you’ve done, what are the things that you are most proud of?

Three or four things that I have done were firsts. One of them is with the motion after-effect. If you have a pattern of bars moving up or down within an aperture and you stop the motion, they appear to be moving in the opposite direction. Nick Wade and I looked at the Falls of Foyers in southern Scotland, which was the first mention of motion after-effect in 1832. We did a lot of work on it. Quite casually, one afternoon when I was working with one of my graduate students, we put out the lights and all you could see was this little aperture with the bars in it moving up and down and, when we stopped it, nothing happened. We were pretty tired, as we had been looking at it all day planning an experiment. So I said, ‘Let’s come tomorrow morning,’ which was a Saturday. We came in the next day and the same thing happened. The answer seems simple now, but it is relative movement. If you don’t have anything to relate to, if they are just bars moving in space, moving relative to you rather than to the surround, you don’t get an effect.

That’s quite important. You could think what happens is that there are cells sensitive to upward movement and cells sensitive to downward movement and you tire out one group of cells and disturb the imbalance.


If that is the explanation, then you should still get the effect in the eye.

That is still referred to. About two or three years ago now, a new book was published on motion after-effects and that gets a real wrap-up. Of course, that had all sorts of implications for the way that visual systems work. I am very pleased about that. That was a high point. Ed Strelow was a very good graduate student and he and I shared the paper which might have been my first paper in Nature, of which there have been about four or five over the years. He moved out of psychology and became an attorney in California. But it certainly put him on the map and it certainly put me on the map.

So that’s the first of the things that you particularly like about your work.

The second thing was that very curious phenomenon where you look through an aperture into a room. The back wall is in this direction (indicates) and the floor is up and down and so on. If you take the front off, the room’s all higgledy piggledy. If you look through a little aperture in the wall, so that you see the inside of the room only, rather than the outside, it looks like a normal room. So a person standing against the back wall looks hugely bigger than somebody in the near space [Ames room].

One of my last experiments at Monash before I left was with a woman who did honours and then her PhD with me. We studied this Ames room very carefully and discovered that it was another instance of perceptual constancy. I haven’t mentioned perceptual constancies, which have always interested me. They are things which remain absolutely constant under certain conditions. The point is that once you block off all the surrounds, you are just looking at the space itself. Again, it is a referential process or experience, and that also got a good deal of publicity in the literature.

What about the work that you’ve done in the area of geometrical illusions?

I think I shall die in an illusory set of circumstances. They have fascinated me all my life. I became interested in them before I had a lab at Monash, and they were things that you could do fairly easily in a room or even at home, if you wanted to. For example if you draw two lines of equal length and you arrange them at an acute angle to each other like that (indicates) and then compare them with the same system so that it is an obtuse angle, the two lines look very much longer than with the acute angle. Now, of course, this is the Müller-Lyer illusion in its fundamental form. No­one had ever bothered to read the original paper by Müller-Lyer. I had it translated and sent to Richard Gregory, who published it straight away. That was a long time ago now. Here are two lines, that are joined together at an acute or an obtuse angle and they look completely different.

Now, this brings it right up to current work. If you leave a little tiny gap between the lines, you don’t get the illusion. So the gap is the critical thing. Think of the number of times in the real world where you see situations or have to do something, where you have gaps rather than joins, I think this is a significant discovery. Again, it is something which came up when I was messing about. I just happened to come across it. And there is a paper which I am writing at the moment which has come out of it.

An edited transcript of the full interview can be found at http://www.science.org.au/scientists/interviews/d/rd.html.

Focus questions

  • What condition or situation is necessary to perceive motion after-effects?
  • Describe the illusion observed in the Ames room. Draw a picture of how two people, at opposite ends of the far wall, would appear to the observer through the aperture.
  • The Müller-Lyer illusion is broken by changing what?

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Select activities that are most appropriate for your lesson plan or add your own. These activities align with the Australian Curriculum strands ‘Science Understanding’, ‘Science as a Human Endeavour’ and ‘Science Inquiry Skills’, as well as the New South Wales syllabus Stage 6 Biology outcome 9.5. You can also encourage students to identify key issues in the preceding extract and devise their own questions or topics for discussion.

  • In the extract, Professor Day discusses three different visual illusions, motion after-effect, the Ames room and Müller-Lyer lines. Ask students to research another illusion e.g. café wall illusion, endless stairs illusion, Ponzo illusion, hollow-face illusion, etc. They should plan and conduct an experiment, using students in the class, family and friends, to test the people’s perception of the illusion. Students should then write a report of their findings, including a statistical analysis of their results. A discussion including an explanation of the illusion and some basics of the neuro-visual system should also be included. (ACSIS199) (ACSIS203)
  • Motion Aftereffect Illusion (Surfing Scientist, ABC Science Online, Australia)
    This demonstration of the motion after-effect illusion includes illustrated instructions, teachers’ notes and links to online versions of the illusion.
  • Construct your own desktop Ames Room (Royal Holloway University of London, UK)
    This pdf contains instructions and a template to create a mini-Ames room. If possible print on A3 or larger paper. Ask students to research the illusion and find an explanation as to why we don’t perceive the true distortion of the walls.
  • Müller-Lyer Illusion (Michael Bach, Universitats-Augenklinik Freiburg, Germany)
    Interactive activity with accompanying explanation of the Müller-Lyer illusion. Extension students might like to look at the research of M.H. Segall, who studied cultural differences in the perception of this illusion. The CSIRO Helix Magazine Teacher Guide for June 2011 has a section entitled ‘Seeing is not believing’ with more activities on visual illusions, including the Müller-Lyer illusion.
  • Lunar Illusion (Science by email, CSIRO Education, Australia)
    This DIY activity from CSIRO Education contains instructions to observe the illusion and an explanation of why we perceive a difference in the moon’s size at the horizon compared to when it’s high in the sky. The dates given to observe the full moon will need to be updated.
  • Professor Day describes himself as an experimental or cognitive psychologist. Ask students to define psychology in these terms. How is it different to a psychological therapist or psychoanalyst? What are some of the challenges for experimental psychologists in terms of experimental design, ethics, cultural influences and reporting bias?  (ACSIS141) (ACSIS199)

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Ames room
Falls of Foyers
geometrical illusion
motion after effect
Müller-Lyer lines
visual illusion

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