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Now let’s think about each oval we will give it a lightish green colour, say, and a size of 10 pixels horizontally and 18 pixels vertically. Next, let’s set the background colour to a uniform darkish blue say. This is probably too small if we were running the experiment “for real”, but it will do for our purposes. Now that we have a qualitative understanding the key components of the stimulus, let’s make them quantitative so we can specify them in our code.įirst, let’s set the overall stimulus size at 400 pixels. Overall, the ovals are presented on a dark lightly-textured background of blues and purples. Looking at each individual oval, we can also see that one side has a white edge and the other side has a black edge. Moving up the rows from the bottom, we can see that the orientation of each successive oval is shifted clockwise from the previous oval. Moving across the columns from left to right, we can see that the orientation of each successive oval is shifted anti-clockwise from the previous oval. On visual inspection of the image above, we can see that it is formed from a grid of green oval shapes. Now we reach the tricky part-how can we create a stimulus containing the illusion?įirst, we need to closely examine our demonstration stimulus and determine its key components.

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Hence, we decide to run an experiment where we manipulate the difference between the intensity of the light and dark regions as our independent variable.Īs our dependent variable, we will have participants rate the subjective experience of motion on a scale from 1 to 5.Īs before, we will work through our experiment framework and build up the code as we go through. We have an inkling that the light and dark regions at the edge of each oval are critical to the illusion. We are interested in knowing what factors in the stimulus lead us to perceive the motion. Perhaps it was motivated after seeing the cover of the album Merriweather Post Pavilion by Animal Collective, as shown below. Our experiment involves a particular visual illusion in which a completely static stimulus appears to be moving, particularly around the time of an eye movement. In this lesson, we are going to work through the process of implementing another experiment in Python and psychopy.

Be able to follow and understand another example of experiment creation and implementation in Python.

Psychopy scale reset