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LuxeSci Show Notes: S1E1 - Plaid

Intro

  1. Hello and welcome to LuxeSci - a podcast to re-ignite your wonder by exploring the intersection of science and luxury

  2. I’m your host, Dr. Lex.  A little about me - I have a Masters in Public Health Microbiology, a PhD in Microbiology and Immunology and over a decade of experience in the infectious disease and global health, working for pharmaceutical companies, non-profits and at the NIH and CDC.

  3. As this is first episode - a few housekeeping items to get out of the way first

  4. I am not an expert in every scientific field but the goal of this podcast is not to go too in-depth on any one topic or to make any of us experts on every scientific field.  The goal is to add a little fun and sparkle to science using relatable items.  So we won’t become experts but we will discover some cool scientific facts and some really amazing linkages between the commercial world and the scientific world

  5. As someone who has spent years learning new things and being told i’m wrong, letting me know i got something wrong or incomplete in a kind and collaborative way - totally cool.  Being snarky or rude about the correction, totally not cool

  1. Plaid Background

  2. I decided to coordinate the first topic with the timing of my podcast launch (because I’m smooth like that) so this first episode is about plaid.  Nothing says “let’s go pick out a pumpkin” to me quite like a good plaid. 

  3. Now, before I can an onslaught (or maybe a tiny ripple) of messages about how plaid isn’t a luxury item, I will refer listeners to the luxury Burberry (based around plaid) the exquisitely cool Alexander McQueen ensemble that SJP wore for the 2006 Met Gala and even to the plaid ensemble that Avril Lavigne wore to this year’s Met Gala.  

  4. As an aside - what is currently defined as luxurious in the US is often done so through a Western/white lens.  Let’s be open to other interpretations of what is luxurious

  5. So back to plaid - i choose this topic for another reason as well.  My maiden name is Scottish and each clan in Scotland has their own tartan (or plaid).  (we’ll get to the difference between tartan and plaid in a bit).  Though apparently a relatively recent invention, Scottish clans each have their own tartan with distinct colors (mine being very green/red).  This is not a history class so i won’t go into the history of Scottish tartans (though it is very interesting).  I will say that it’s kind of cool to have a family tartan

  6. Plaid vs tartan

  7. According to the ever ubiquitous and mostly reliable source, Wikipedia tartan is “alternating bands of colored threads woven as both warp and weft at right angles to each other (assuming warp and weft are weaving terms).  This forms visible diagonal lines where different colors cross, giving the appearance of new colors blended from the original ones”.

  8. Plaid was a large piece of tartan cloth worn as a type of kilt or shawl

  9. Since we’re here in the US and Americans love to alter meanings of things, especially historical meanings, i’m going to use plaid to mean the pattern

  10. So what do plaid and science have in common.  It turns out that plaid is used by researchers to discover how our visual processing system recognizes certain patterns.  

  11. I love anything to do with the brain but i have to say that this has been one of the hardest topics i’ve researched lately.  The visual processing system in humans is very complex and the jargon for this field of research is akin to reading a foreign language

  12. But let’s go on this learning journey together - at the very least you can sound super impressive at your next cocktail party when someone is wearing plaid by saying “did you know that plaids are used in visual processing research?”  ---- that is if you hang out with nerdy people like i do

  13. Visual processing

  14. OK, before we dive into all things plaid, let’s review visuall processing basics (or in my case totally relearn because despite dissecting a lot of pigs in biology, my knowledge of brain anatomy is extremely low) 

  15. The visual cortex is the part of our brains responsible for processing visual information.  It’s located in the occipital lobe (in the back near the base of our skull).

  16. Information arrives at the visual cortex via lateral geniculate nucleus (through the thalamus)

  17. There are six different areas (v1-v6) to the visual cortex and two main “streams” of information through those areas

  18. Ventral stream - associated with form recognition and object representation

  19. Dorsal stream - associated with motion control of the eyes and arms , representation of object location

  20. Neurons in the visual cortex fire action potentials (nerve impulses) when certain stimuli arrive in the receptive field

  21. There is a hypothesis called neural toning which posits that neurons selectively respond to specific patterns through experience

  22. Example, the V1 neurons have been found to be tuned to certain orientations, sizes, positions and forms (Hubel DH, 1959)

  23. So those are the basics.

  24. One other topic we need to review before moving onto the plaid research is filters.  (many thanks to: https://www2.aston.ac.uk/migrated-assets/applicationforce-download/lhs/30846-Filter%20tutorial%207.pdf )

  25. So what is a filter?

  26. “Something that receives input and passes on some of the input as an output..think a sieve or strainer”

  27. If we’re talking about image processing than both the input and output are images so what gets filtered?

  28. It turns out that human eyes filter out high spatial frequencies from the input they receive.  It would seem that filtering out information would be detrimental to sight but it turns out to be a good thing as the spatial frequencies that are filtered out would not be used by your visual processing system anyway and would just be clutter

  29. Now - there’s a very scientific explanation of this phenomenon but I’m going to take points from this amazing tutorial that i found.  Remember when we were kids and we used to make mix CDs for all our besties, romantic interests, road trips, etc? So the input signal here (music) might contain audio frequencies that are higher than the frequency used to make CDs (and also can’t be heard).  If those higher frequencies aren’t removed, they would produce low frequency aliases that produce auditory interference.  

  30. So - much like a CD (I know, ancient technology), your eyes apply filters to spatial information to reduce clutter and interference


  31. The role of plaid

  32. Wow - that was a ton of background but we made it through.  Any questions?  No?  OK, let’s move on.

  33. I think we can now finally get to the plaid...whooo hooo!

  34. Plaid has been used for some time in the field of visual processing research to understand how your eyes and mind see and comprehend patterns and how those filters I mentioned before are used in image processing

  35. In one experiment by Georgeson et al in 1997, plaids were stretched and filtered with various parameters and shown to participants who classified the appearance of the plaid into one of two categories (for example, square or diamond).  The researchers found that components of plaids are visually combined in a variety of ways and that neurologically humans selectively group and combine the outputs of oriented spatial filters to achieve these different visual perceptions of plaids.  

  36. Pause - is everyone still with me?  A little recap.  So far we’ve learned that visual processing happens in the visual cortex of the brain and that our visual processing systems use filters to block information that would not get used and would create interference.  Additionally, these spatial filters are grouped and combined to achieve different visual perceptions (and plaid helped researchers figure that out)!

  37. Researchers have moved from stationary plaids to looking at the perceived motion of plaids.  We’re going to take a quick tangent to get some background on motion perception (which means we’re back to Wikipedia and looking at the dorsal stream, remember that from before?).  Motion perception is inferring the speed and direction of an object based on various inputs.  Motion perception is a part of human eyesight that has been challenging to unpack for researchers.

  38. I’m going to be really simplistic with this explanation in the interest of time and because the theories on motion detection are still hotly debated (trust me, scientific debates about obscure things can get super tense)

  39. First-order motion perception contains both beta movement (or apparent movement) where stimuli being switched off and on alternatively give the illusion of movement (think racing Christmas lights).  Fun fact - this is the basis of television.  The phi phenomenon happens when the distance between stimuli is just right and the alternation is faster and produces an effect of an “object” moving quickly between points and occluding the stimuli (think something akin to strobe lights).  One current model of how this all happens is that there are motion sensors in the visual system that detect a change in luminescence on on part of the retina and an correlate it with a change in luminescence on a neighboring part of the retina with a short delay (like the racing Christmas light model).

  40. Second-order motion perception is when the moving object is characterized by a feature other than changing luminescence (i.e. contour, texture, etc).  

  41. Third-order motion perception is a kind of mapping exercise where motion of objects is defined as marked or unmarked.  Kind of your brain making a map, pinning some things as constant and detecting motion based on those constants

  42. In summary - in early visual processing, 3 independent systems extract motion information from visual inputs and they are combined at a later state (Sperling et al)

  43. Back to the research: Sperling et al wanted to look at how motion is visualized in plaids… you know when you used to stare at pattern long enough and it seemed to move.  That is a common trick with plaid visualization.  So taking data from a large dataset on plaids and visualization, the researchers found that only 2 out of the 3 motion perception systems respond to plaids (systems 1 and 3) and that response includes direction and not speed.  This led the researchers to hypothesize that motion direction and speed are processed independently in early visual processing.

  44. You may be thinking right now...what exactly did i get myself into listening to this podcast?...or...knowing how we see is all well and good but what difference does it make?  Research published in 2008 in Graefe’s Archive for Clinical and Experimental Ophthalmologyby Eisenbarth et al,  used plaids to investigate motion contrast sensitivity in subjects with age-related maculopathy (a degenerative disease of the retina).  The scientists set up a testing apparatus that consisted of a white screen with a rectangular cut-out and an LED screen in that cut-out where the images were projected.  Participants were asked to identify the direction of motion of patterns from a fixed reference point.  That part doesn’t sound particularly fancy but there was a fair amount of fancy math that went into the analysis.  Additional tests were run to measure color perception, flicker frequency double-pulse resolution (measuring multiple visual field positions at once).  The researchers found that patients with ARM had a severely impaired central visual field, which is beyond the borders of the macula where the disease is thought to occur.  Essentially, the science showed that visual perception was impaired beyond what had been previously thought for this condition.  This was thought to be a critical finding since although these perceptual limitations may not be evident to people with ARM, they are important for safe mobility and driving a car.  The sample size (n=18) was relatively small so confirmational studies would need to be done but it does show how plaid is used in research to better understand visual perception impairments

  45. One completely different bit of research i found in my investigations is a study in 2020 by Koo et al and published in the Journal Evidence Based Complementary and Alternative Medicine.  Here, the researchers had 120 older adults in Taiwan randomly assigned to engage in mandala coloring, plaid coloring, free-form drawing or a reading groups for 20 min.  The researchers measured each participants’ anxiety levels using a validated scale at baseline, after a brief anxiety induction and at the end of the assigned activity.   Although plaid coloring did not turn out to be anxiety reducing in this study, mandala coloring did so next time you’re stressing out about something, maybe find a mandala to color

  46. I hope that you’ve found this little foray into visual processing research to be as fun as i have and that the next time you see Burberry print or a plaid scarf - you’ll think about spatial orientation filters.  

  47. Thanks for listening to this inaugural episode of LuxeSci.  A very special thank you to my audio engineer, Dimos.  Our theme music is Harlequin Moon by Burdy. If you have a correction, comment or praises, you can reach me at: drlex@luxesci.com.  We on twitter at luxescipod and Instagram at luxescipod.  If you like us, please subscribe.   Please also leave us a review where ever you listen to podcasts.  See you again in 2 weeks!



References:

  1. Tutorial Essay on Spatial Filtering and Spatial Vision - Tim S Meese School of Life and Health Sciences Aston University, March 2009 https://www2.aston.ac.uk/migrated-assets/applicationforce-download/lhs/30846-Filter%20tutorial%207.pdf 

  2. Perception of Stationary Plaids: The Role of Spatial Filters in Edge Analysis. Georgeson MA and Meese TS. Vision Research (1997). 37(23) pp 3255-3271

  3. Adaptive Filtering in Spatial Vision: Evidence from Feature Marking Plaids. Georgeson MA and Meese TS. Perception (1999). 28(6)

  4. Characteristics of dynamic processing in the visual field of patients with age-related maculopathy. Eisenbarth W, et al Graefes Archive for Clinical and Experimental Ophthalmology (2008). 246(1): 27-37

  5. Coloring Activities for Anxiety Reduction and Mood Improvement in Taiwanese Community-Dwelling Older Adults: A Randomized Controlled Study. Koo M, et al. Evidence Based Complementary and Alternative Medicine (2020).

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