Phil Gyford


Friday 15 April 2005

PreviousIndexNext Mind Hacks by Tom Stafford and Matt Webb

Finally got round to reading it and wasn’t disappointed. Very dense with interesting nuggets. The notes aren’t a summary of the whole book; more the bits that I found most interesting or that were most new to me.

1. Inside the Brain

5 Electroencephalogram (EEG) produces a map of electrical activity on surface of brain. Good time resolution, cheap, poor spatial resolution.

6 Position Emission Tomography (PET). Inject radioactive chemical into bloodstream, watch where it ends up. Produces 3D model, bulky, expensive, resolution only shows activity about 1cm across. No good for change over time.

7-8 Functional Magnetic Resonance Imaging (FMRI). Lie inside electromagnet. High spatial resolution (2mm), snapshot every 2 seconds or so, bulky, expensive.

9-12 We don’t “only use 10% of our brain.” There is no part of the brain that doesn’t “light up” in response to some task or other. If there were really neurons that weren’t used, they would probably have stopped working — become useless — in puberty. Although Glial cells, which play a supporting role to neurons make up 90% of the brain.

19-20 A neuron is a cell body with long offshoots. Signals pass one way along it: into the dendrite offshoots, out of the axon offshoots. Junction between one cell’s axon and another’s dendrite is the synapse. Neurons are binary and information is encoded in the rate at which they send signals.

22 The brain uses 20% of the body’s oxygen.

25 We respond quicker and more firmly for bright lights/louder noises.

2. Seeing

34 Just behind the eyes, the optic nerves join at the optic chiasm. The right halves of the two retinas lead to left part of the brain and vice versa. Allows for depth information to be created.

38 The fovea is the centre of the retina, with the highest resolution. It’s small: look at the night sky and the fovea just covers the moon.

40-41 Cones are at the highest density in the fovea and drop away very quickly. They work best in light conditions and respond to colour (we can’t see much colour outside the centre of vision). Rods are more numerous outside the fovea. They’re sensitive to light (not colour). Good in dim conditions. In dark conditions the cones shut down over five minutes. Rods become most sensitive after half an hour. The rods are densest just outside the fovea, so the best way to spot faint light (e.g., stars) is to look slightly off-centre.

43 Eyes constantly shift their view, the shift’s called saccades. Up to five times a second. Movement is unconscious. Each pause is a fixation. Speed-reading involves reducing the fixations per line of text — ideally to one.

48 Octopus eyes evolved independently and have no blind spot — the retinal cells have the photoreceptors in front of the nerve fibres, not behind.

50 When your eyes saccade your vision blanks — which is why you can’t see your eyes move in the mirror.

52-4 Explains why second hands on clocks sometimes seem to freeze when we glance at them — the brain assumes the hand has been where it is since our eyes started moving, to make up for the blank saccade time.

57-61 We assume light comes from the top of our field of vision, and interpret flat-but-shaded shapes accordingly. Actually, we assume light comes from top left. Don’t know why it’s left.

66-7 Five cues we use to determine depth: binocular, perspective, occlusion, focus, motion.

74 Luminance is a physical measure. Brightness is our subjective interpretation, constructed from experience — checker shadow illusion: the squares have the same luminance, different brightness.

85 Perhaps why public mobile phone conversations are so distracting: Normal conversations have a more constant volume, timing and rhythm, and we adapt. But on the phone we get no cues from the distant speaker so we can’t subconsciously predict when near speaker will talk. Hard to automatically filter out this irregular noise.

104 It’s easier to imagine yourself rotating/moving around an object than it is to imagine the object rotating/moving.

106-7 Our very fast startle response (within 80ms) occurs when we see symmetrical expansion of darker-than-background areas.

3. Attention

114 “We’re better at making out detail in the lower half of vision — the resolution of attention is higher there.”

117 Russian abaci have the two central beads on a row of 10 coloured differently. Splits row into 3 groups with maximum of 4 beads each, making it easy to subitize (knowing how many items are there by looking at the group, rather than counting each individually — works for up to about 4 items).

124 After leaving the eye, visual information divides. Our conscious appreciation of the information happens in the occipital lobe. Attention capture happens in the superior colliculus — evolutionary, ancient, unsophisticated but very quick reflex movements.

126 Blindsight occurs when the former is damaged — person believes they’re blind but can still, say, reach for a bright light because they see it subconsciously.

129-134 Attentional Blink: If you have to, say, spot two items from a list/sequence, you may well miss the second if it appears very close after the first (a simplification of the explanation).

4. Hearing and Language

154-5 A sound has a main vibration — its pitch. Will be accompanied by secondary vibrations at higher frequencies, called harmonics. These vibrate at frequencies which are integer multiples of the fundamental frequency. The pitch of the sound we hear is based on the fundamental frequency, no matter what the harmonics are. Even if the fundamental frequency isn’t part of the sound we hear, we still hear pitch based on what it should be.

So for a sound that repeats four times a second but that is made up of component frequencies at 8 Hz, 12 Hz, and 16 Hz, the fundamental is 4 Hz, and it is based upon this that we experience pitch.

6. Moving

209 Ramachandran and Rogers-Ramachandran, helping amputees with phantom limb pain. Reflecting their intact limb in a mirror provides enough info to the brain to make it feel like it could control the missing limb and “move” it out of a position that had been causing them pain.

226-9 Left brain: Sensations from right side of body; “inventive and interpreting”; structure and meaning; high-level associations and problem solving, including language, looking for meanings and patterns; better at processing rapidly occurring sounds and keeping rhythm; speech and (usually) understanding literal meanings of words and sentence grammar; better at sequential ordering and symbolic logical reasoning.

Right brain: “truthful, literal”; preoccupation with general surface features; “modules specialising for computationally analysing perceptions, in a very straightforward way, not looking for any deeper meaning”; “May support analysing global features of language such as mood and implication”; “visual and spatial processing, such as mental rotation or remembering maps and faces, dealing with the appearance of things, and with understanding the overall patter”; dominant in perceiving gender and moods; musical appreciation.

7. Reasoning

232-3 When estimating numbers, most people start with a figure that comes easily to mind and adjust up or down from that. So can be swayed by giving them an “anchor” first. e.g., charities asking for donations of $50, $20, $10, $5, not $5, $10, $20, $50.

8. Togetherness

270 Ideomotor effect — when we cause something to happen but don’t think we have, e.g. Ouija boards, dowsing wands.