Author: tom

A neat little effect:

Moore says,

If two successive sounds are heard as fused, the location of the total sound is determined largely by the location of the first sound. This is known as the “precedence effect”, although it has been called the “Haas effect”…

This, among other things, stops you getting confused when a sound comes at you from two speakers at once.

Now, if you drop something and record the sound, and then play it back backwards, you can hear the echos that are normally masked.

(Thanks to Nicol, and his supervisor, for the info)

There is more, of course, in the book

Ref:
B.C.J. Moore, An Introduction to the Psychology of Hearing, 5th Ed., Academic Press, San Diego (2003).

What has psychology done? A challenge to silence the doubters comes from the BPS in this Month’s issue of The Psychologist

The Society’s Publications and Communications Board would like to produce a new document to complement the Annual Report, focusing on psychology rather than the Society. This report would outline significant scientific research developments and practical applications from the discipline in the last year.The aim is to promote the usefulness of the discipline to an external audience of research councils, politicians, civil servants, employers and journalists. Before potentially producing this as a separate document in 2006 we would like to pilot the project as a special feature in The Psychologist. Your contributions are sought. We are looking for brief descriptions of:

published research from the last year

partnerships between academia and the public or commercial sector leading to new products or applications of psychological knowledge; or

new professional developments which will have a significant impact on the lives of others.
…you could even just send one sentence on what has been found, one on why it is important in terms of understanding people or making a difference to their lives, plus the reference. Material has to be intrinsically relevant and interesting to an extremely wide audience with little or no background knowledge of the area, and written in a way that makes it more so. It is a tough task, but this is a great opportunity to show what psychology has been up…This is your chance to silence the psychology doubters by showcasing interesting and useful research from the last year, so get writing. Send your contribution to jonsut@bps.org.uk by Monday 15 November. Feel free to get in touch before then if you have any questions about the process or the suitability of material. [my emphasis]

Real laziness here, stealing notes from a review of a book that I can’t be bothered to read
The Book: The Wisdom of Crowds: Why the Many are Smarter than the Few by James Surowiecki
The Review: London Review of Books. The Notes: gyford.com

Phenomenon: For many decisions the average of many judgements is often better than the judgement of a single, albeit expert, individual. Example: judging the number of jellybeans in a jar – typically even individuals who have previously been most accurate (‘the experts’) will be outperformed by the average answers.

Seems analogous to the ‘less is more’ effect. This is, roughly, that sometimes an overabundance of information can distract you from applying an on-average-correct heuristic. Example: Answer this question Which city has more inhabitants: San Diego or San Antonio?. Who should do better at this question, Germans or Americans? The Germans, typically, have little knowledge of the size of American cities. So when given this pair they guess that the one they have heard of is larger (San Diego), and they are correct. The Americans know lots about American cities. They try to use all the information they have to make a correct decision. Which is more politically important? Which has more people I know living in it? Which felt bigger when I visited? Sometimes this information is helpful, sometimes it is distracting. Sometimes decision making based on more knowledge is outperformed by that based on less knowledge (here the analogy with the wisdom of crowds i guess). In one study [1] the German group using their simple recognition heuristic scored 100%. More generally, often neither method/group is always correct, but the simple, one criterion, rule can often be more correct.

So one mechanism by which the wisdom-of-crowds effect works is probably just reducing the level of knowledge that is contributing to the decision. A dumb kind of wisdom!

But crowds can often be dumb-dumb too, especially when they become herds. What are the conditions under which they keep their dumb-wisdom, the conditions when a mixture is better than the best expert?

Quoting gyford.com

Requires certain conditions for the crowd to make good decisions: members of group must be willing to think for themselves; they must be mostly independent of each other; must be reasonably decentralised; must be some means of aggregating opinions into a collective judgement. If people start second-guessing each other, or following each other, the crowd becomes a herd and herds are bad at decision making…Crowds do not do well the question is not a straight-forwardly cognitive one. They are not good at moral judgments.

You might argue that a group of people which are all thinking for themselves isn’t really a crowd. You might also argue that the wisdom of crowds doesn’t apply to moral judgements because individual judgements are non-commensurable in so many ways, not just because they are subject to lots of weird biases. If the choice is the same, but the individuals are making different decisions (e.g. they have access to contradictory information and/or they are using different criteria to select what a ‘good’ answer is) then aggregation isn’t possible.

I think a more helpful book would not be The Wisdom of Crowds – Why the Many are Smarter than the Few but The Wisdom of Crowds – How the Many can be Smarter than the Few. Anyway, good to have some starting notes on when crowd decisions will outperform individual decisions – and when ’emergent’ decisions will be herd-like and unproductive.

Refs

[1] Goldstein, D. G., & Gigerenzer, G. (2002). Models of ecological rationality: The recognition
heuristic. Psychological Review, 109, 75-90. Online here

A wrinkle to add to one of my favourite neurobiology factoids: Dolphins may not sleep with one side of their brains at a time after all [1]. Or, rather, they do sleep one side at a time (unihemispherically), but they may also sometimes let both sides sleep at once, albeit very briefly.

It’s not just dolphins who sleep with one side of the brains at a time. Other sea-sleeping mammals (whales, seals and manatee), many birds and maybe reptiles, like crocodiles, sleep unihemispherically too [1].

Posture assumed by northern fur seals during unihemispheric slow-wave sleep in water. In this example, the fur seal is lying on its left side while the left flipper (connected to the awake (right) hemisphere) constantly paddles. This posture allows the fur seal to keep its nostrils above the water?s surface, while the left hemisphere sleeps. When the fur seal switches to lying on its right side, the left hemisphere remains awake while the right hemisphere sleeps. (Figure and text shamelessly stolen without permission)

So: possibly our reptilian ancestors slept unihemispherically and we lost the habit as we tripped up the phylogenetic scale. Secondly, dolphins probably wouldn’t sleep one hemisphere at a time if they weren’t sleeping in the water. If we could just convince those guys to move onto land…I mean they’re pretty smart already, think what they could do if they could let one of their hemispheres drop the functions needed for wakefulness [3]. With one hemisphere relived of the need to be self-sufficient it could develop a deeper, complementary role for the other, waking-responsible hemisphere. They could be even smarter than they already are. Lets face it, we could do with some help up here- we need the dolphins on our team!

Hmm. Anyway. I wonder if there asymmetries in the human hemispheric response to sleep? It would suggest that a similar process had happen in mammalian evolution. And did dolphins evolve from a land-based mammalian line, and when?

Refs

1. Sam H. Ridgway (2002). Asymmetry and Symmetry in Brain Waves from Dolphin Left and Right Hemispheres: Some Observations after Anesthesia, during Quiescent Hanging Behavior, and during Visual Obstruction. Brain, Behavior and Evolution 2002;60:265-274

3. Incidentally dolphins do have some hemispheric specialisation – they have a left dominance for visuo-spatial cognition (ie the opposite to humans): Kilian, A., von Fersen, L., G?nt?rk?n, O. (2000). Lateralization of visuospatial processing in the bottlenose dolphin (Tursiops truncatus). Behav Brain Res 116: 211-215

My friend Nicol had his first paper in Nature come out today [1]. Well done Nicol! [2]. For any readers who care for a bit of computational neuroscience, with information theory on the side, here’s the abstract:

A sound, depending on the position of its source, can take more time to reach one ear than the other. This interaural (between the ears) time difference (ITD) provides a major cue for determining the source location. Many auditory neurons are sensitive to ITDs, but the means by which such neurons represent ITD is a contentious issue. Recent studies question whether the classical general model (the Jeffress model) applies across species. Here we show that ITD coding strategies of different species can be explained by a unifying principle: that the ITDs an animal naturally encounters should be coded with maximal accuracy. Using statistical techniques and a stochastic neural model, we demonstrate that the optimal coding strategy for ITD depends critically on head size and sound frequency. For small head sizes and/or low-frequency sounds, the optimal coding strategy tends towards two distinct sub-populations tuned to ITDs outside the range created by the head. This is consistent with recent observations in small mammals. For large head sizes and/or high frequencies, the optimal strategy is a homogeneous distribution of ITD tunings within the range created by the head. This is consistent with observations in the barn owl. For humans, the optimal strategy to code ITDs from an acoustically measured distribution depends on frequency; above 400 Hz a homogeneous distribution is optimal, and below 400 Hz distinct sub-populations are optimal.

Update: Article from BBC news Hearing more complex than thought

Refs
[1] Optimal neural population coding of an auditory spatial cue
Nicol S. Harper and David McAlpine
Nature, 05 August 2004, Volume 430, No. 7000, pgs 682-686

[2] I am immensely proud – in the it-had-nothing-whatsoever-to-do-with-me-I-just-watched-it-happen kinda way