Second-order change blindness

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In recent talks in Warsaw (IACAP) and Krakow (ASSC), I sketched some experimental designs that would allow us to see whether visual experience is backward-looking or forward-looking (do we experience things as they were, or as they will be? Or neither?).  When I shared the early form of these designs with Matt Jaquiery a few years back, he pointed out that they assumed an affirmative answer to a question which had not yet been answered (or asked) in the experimental literature: do people suffer from change blindness with respect to second-order spatio-temporal visual properties?  Specifically, will the usual distractors (white flash, “mud splashes”, etc) result in subjects failing to notice a change of trajectory of a visual object?  Matt then designed and conducted a web-based experiment to answer this question.  Nora Andermane helped out by running a lab-based version.  The answer is yes.  A paper presenting our results is now under review with PLoS ONE.  The bioRxiv preprint (“Trajectory changes are susceptible to change blindness manipulations”) is available now (comments welcome!):

Here’s the abstract:

People routinely fail to notice that things have changed in a visual scene if they do not perceive the changes in the process of occurring, a phenomenon known as ‘change blindness’. The majority of lab-based change blindness studies use static stimuli and require participants to identify simple changes such as alterations in stimulus orientation or scene composition. This study uses a ‘flicker’ paradigm adapted for dynamic stimuli which allowed for both simple orientation changes and more complex trajectory changes. Participants were required to identify a moving rectangle which underwent one of these changes against a background of moving rectangles which did not. The results demonstrated that participants’ ability to correctly identify the target deteriorated with the presence of a visual mask and a larger number of distractor objects, consistent with findings in previous change blindness work. The study provides evidence that the flicker paradigm can be used to induce change blindness with dynamic stimuli, and that changes to predictable trajectories are detected or missed in the similar way as orientation changes.


What is colour?


Fellow Sackler member Jim Parkinson brought to my attention the fact that this year’s Flame Challenge – explaining science to 11-year-olds in less than 300 words – is on the topic “What is Color?”.  I decided to take up the challenge; here’s my entry (299 words!):

The question “what is color?” is tricky.  Understood one way, it hardly needs answering for people with normal vision, who have no problem learning how to use the word “color” and what the names for different colors are: color is just part of the way that things look.   But that answer would be of little use to a blind person, since for them objects don’t “look” any way at all.  Science should try to explain things for everyone, so here’s an explanation of color that works for all people, sighted or blind.
Light is a collection of extremely small particles called photons. A photon might begin its journey at a lamp, bounce off an object (such as a book), and end its journey by being absorbed by one of the cells that line the back wall inside your eye.  Photons wiggle while moving – some wiggle slowly, some quickly.
The color of an object is the mixture of wiggle speeds of photons the object gives off in normal light. 
Sighted people can see an object’s color because the way a photon affects their eye cells depends on its wiggle speed.  For example, if your eye absorbs a slow wiggling photon, you see red; a fast wiggling photon, you see blue. Mixtures of wiggle speeds have a mixture of effects on your eye cells, letting you see a mixture of colors.  Something colored white gives off photons of all wiggle speeds.
If you shine red light on a white ball it looks red, but its actual color is still white because if it were in normal light it would give off photons of all wiggle speeds.  Similarly, a blue book in the dark is still blue because it would still give off fast wiggling photons were it in normal light. 

Comments welcome.