Monthly Archives: October 2013

Neuronal models of motion sensitivity

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I was just assembling a (personal, biased) reading list on neuronal models of motion sensitivity, and it occurred to me it might be good to do it publicly as a blog post. Please any neuro readers, chip in with your own contributions!

Books

Landy & Movshon (eds), Computational models of visual processing

Russell & Karen DeValois, Spatial Vision

Concepts

Zanker, J., Modeling human motion perception. I. Classical stimuli. Naturwissenschaften, 1994. 81(4): p. 156-63.
I think this might be a good place to start – what do you reckon?

Models of simple motion sensors

roughly corresponding to V1 in my mind.

Adelson, E.H. and J.R. Bergen, Spatiotemporal energy models for the perception of motion. J Opt Soc Am [A], 1985. 2(2): p. 284-99.
Poss my all-time fave in the genre. So clear and logical.

Watson, A.B. and A.J. Ahumada, Jr., Model of human visual-motion sensing. J Opt Soc Am A, 1985. 2(2): p. 322-41.
van Santen, J.P. and G. Sperling, Temporal covariance model of human motion perception. J Opt Soc Am [A], 1984. 1(5): p. 451-73.
van Santen, J.P. and G. Sperling, Elaborated Reichardt detectors. J Opt Soc Am A, 1985. 2(2): p. 300-21.
Three more classics.

Perceptual consequences of this sort of motion sensor:

Sheliga, B.M., et al., Initial ocular following in humans: a response to first-order motion energy. Vision Res, 2005. 45(25-26): p. 3307-21.
Such a nice demo with the missing-fundamental stimulus.

Serrano-Pedraza, I., G. P., and A. Derrington, Evidence for reciprocal antagonism between motion sensors tuned to coarse and fine features. Journal of Vision, 2007. 7(12): p. 8 1-14.
Intriguing result and nice clear modelling

What does MT do differently?

Heeger, D.J., E.P. Simoncelli, and J.A. Movshon, Computational models of cortical visual processing. Proc Natl Acad Sci U S A, 1996. 93: p. 623-627.
Getting into the difference between V1 and MT, pattern vs component motion etc

Perrone, J.A. and A. Thiele, Speed skills: measuring the visual speed analyzing properties of primate MT neurons. Nat Neurosci, 2001. 4(5): p. 526-32.
How do you get a neuron tuned to speed from neurons tuned to spatial and temporal frequency?

What do you reckon, vision science community? What must-read papers did I miss out?

Of nature and nurture

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I’m no geneticist, but I was interested to see the recent comments on the heritability of academic performance. I thought it demonstrated the sorry lack of understanding of these things in the media and general public (including me), and I was disappointed in the quality of the debate.

A government advisor, Dominic Cummings, wrote a report in the course of which he stated that “70% of cognitive capacity is genetic, beside which the quality of teaching pales into insignificance”. This got a lot of comment, e.e.g from Polly Toynbee in the Guardian. Toynbee does make clear that she doesn’t understand genetics, and seeks advice from genetics Prof Steve Jones. I eagerly heard a discussion of this on the BBC Radio 4 programme “Inside Science” between Profs Jones and Plomin, hoping they would give a clear explanation of what exactly heritability is which would help people like me.

For example, Toynbee says at one point, “Wealth is considerably more heritable than genes”. This is obvious true in an everyday interpretation of the word – you can will your millions to your children, but you can’t guarantee they’ll inherit your striking red hair. But in the scientific definition of the word, nothing is more heritable than genes. I felt this demonstrated the confusion, and this is where we really needed a nice BBC science programme to go into these issues.

Despite the august guests, I felt they didn’t really rise to the occasion. I’m no expert, but I find it helpful to realise that when we talk about heritability, we’re not talking about a fixed quantity, like the mass of the electron. It depends on the context. It may be 70% in Britain now, but it might have been 20% in the past and 90% in Finland. If you just consider one school where the kids come from similar backgrounds, the heritability may be close to 100% – there are bright kids and dimmer kids even within the same family, and it’s just how they are. But if you look between schools, comparing privileged vs deprived kids, you might find the variation between kids in each group is swamped by the large difference between the groups, indicating almost no heritability and an overwhelming effect of the environment.

The closest the discussion got to this was a throw-away comment by Steve Jones: “If everyone stopped smoking, lung cancer would be a genetic disease”. I thought this was an important point which should have been pursued: if we could arrange things so that every child could get the best possible education to enable them to achieve their potential, academic performance would be 100% genetic.

Finally,as far as I remember, no one stated that heritability has nothing to say about the importance of teaching quality, class size, resources and so on. If we find academic performance is 100% genetic, that indicates variation in these factors is not affecting results: children are receiving the same opportunities. But they may not be receiving the best opportunities.

As I said above, I’m not a geneticist, so I’d welcome any correction if I’ve got the wrong end of the stick anywhere in the above…

British Science Festival

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This has been an exceptionally good and fun week doing the British Science Festival. Lisa had set up a workshop all on camouflage and mimicry and during all the lab helped out (although kudos to Lisa who managed to do every session with a big smile on her face!). There were lots of different activities to do during the workshop including a load of real life creepy crawlies that were all experts at camouflage. My task was to take the children through some posters and do some questions on a quiz sheet. The first question was to do with mimicry. I explained that a hoverfly pretends to be a wasp so that it doesn’t get eaten by birds and we had three example hoverflies from different species trying to mimic a wasp. The children had to rank them in order of ‘most waspishness’ and everybody agreed one was rubbish, one was good, and one was OK. They found it very interesting that birds actually saw our OK mimic as a good mimic and our good mimic as an OK one, and some even ventured a guess that it meant birds see things differently from ours.

Next up on the quiz was aposematism. For those that don’t know, aposematism is the act of being very bright and colourful to warn predators away from eating them, we had examples such as a bee (black and yellow, ‘I’ve got a stinger leave me alone’), a poison arrow frog (Black and yellow patterns ‘don’t eat me I’m poisonous’) and the bombardier beetle (red and black ‘don’t eat me or I’ll spray you with a horrible stink, the kids particularly loved this one!). As a group we then discussed other aposmatic creatures. I had some very interesting answers, of which most were brightly coloured but more to stay camouflaged (tiger, zebra and clown fish). I had some that were mimics or dangerous in their own way (milk snake and sea anemone) and some really good answers (ladybird, skunk, wasp, ringed octopus).

The final two questions involved matching the creature to the type of camouflage it was using, and then guessing which out of 14 butterflies were poisonous and tasty. After the quiz was finished the kids rotated and did something else in the room (which you will probably hear about in other blog posts) and I started again with the next group.

The entire workshop was a great success and I really think some kids took some real knowledge and interest away from the day, and I heard more than one say it had been the best one they had seen yet. Very pleased I volunteered to help out with the event!

Tying up some loose ends

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While I wait to begin construction of my next experiment (assessment panel approval pending) I have been working hard on various different bits and pieces. My paper for the oblique angles study is almost ready for submission (bar the inevitable red pen from Jenny, and a results section that is still half-written as we finish analysing the results) and I am pleased with the progress. With the analysis we have constructed various models to try to map the data, with my personal favourite being a combination of two Gaussian curves, and others including absolute values (which means the magnitude of the number only, not the sign, for example the absolute value of -2 is just 2) and polynomials (terms with powers, such as squared and cubed etc.).

Jenny and I are discussing these later this week, to decide which is the best to model the data. We have assessed the significance using SPSS already so all we really want is a nice smooth model to represent the data well. I am thrilled to announce we do have significant results however, which is something scientists always like to hear! While I don’t agree with the practice it seems to me a trend in journals is that significant results get published much more. Probably because significance proves something, where a lack of significance, by definition, proves nothing.

For example if you spin a 5 coloured spinner and say ‘it is definitely red’ – then you have a result (red). However if you say ‘it is not definitely red’ you cannot say anything about the results. It may in fact be red. But even if it is not you have no idea what colour it really is.

I can see the argument for such papers (definitely red) getting preference but I do believe scientific research would develop much quicker were all the non-significant tests and results published, even somewhere open access like wikipedia. If only to check nobody has already tried what you’re thinking of and failing. Such a site may indeed exist but I haven’t heard of it. Some non-significant result papers do make it in if they are well written or have original methodology, but the habit of selecting significant papers is one I think sometimes hinders scientific development. Just my opinion.

Wow got a bit sidetracked there! So while waiting for my next experiment to be approved and set up I have also submitted my paper on oblique angles to IC3D to see if they would like me to present (still waiting to hear from them) and I am presenting a poster twice in the space of a week! Once at an internal ION event (postgraduate poster evening, should be fun) and NEPG2013 (6-university wide event where postgrads can submit, and I was selected. Much more formal and a bigger deal!) So I am looking forward to that.

Lastly I have assembled my team of supervisors properly for my PhD. Tom Smulders, who did animal behaviour with me in my MRES year, and Vivek Nityananda, a member of the lab, will join Jenny in making sure my PhD goes without a hiccup!

Mantis in motion

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Things are going well with the mantids. They are such great experimental subjects; I think I prefer them to humans! Certainly a lot less hassle :).

Although the main thrust of the M3 project will be about their stereo vision, we are getting increasingly excited about the great questions we can ask about their motion perception. Lisa is currently collecting data on a motion perception question, while Vivek is progressing the main stereo research arc by constructing ever more refined 3D glasses for the mantids. Ghaith is working on stimulus generation for both projects and starting to develop models of the underlying algorithms. Exciting times.