ch 31 Sensation & Perception Ch. 3: Vision © Takashi Yamauchi (Dept. of Psychology, Texas A&M University) Main topics –convergence –Inhibition, lateral inhibition and lightness perception –Interactions between neurons –Feature detectors

ch 32 Question 1 What do these devices have in common?

ch 33 These devices make use of electromagnetic waves Capture electromagnetic waves and transform them into electricity.

ch 34 What does the eye do?  Transducing light energy into electrical energy

ch 35 Transduction  Light enters the eye  A photon hits a receptor  changes the shape of pigment molecules  triggers massive chemical reactions  generate electrical signals

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How big are they? –Power of Ten (10 min) – _embedded&v=0fKBhvDjuy0#! ch 37

8 Solar cells (photovoltaics) produce electricity in a similar way as our eyes do.

ch 39 Rods and cones Morphology Distribution on the retina Dark adaptation Spectral sensitivity

ch 310 Photo receptors: Rods and cones Rods have bigger outer segments than cones. Why?

ch 311 Outer segments capture photons Bigger outer segments can capture more light. Rods have bigger outer segments. –Rods allow us to see in the dark. –Cones are mainly for day vision. –Cones are for color perception.

ch 312 How can we see a book? How can we see a desk? Why don’t we see light? How can we see objects?

ch 313 Reflection of light What we see is a reflection of light. Different objects reflect different wavelengths, –  different objects show different colors

ch 314 Photo receptors in the eye are geared to capture different wavelengths

ch 315 Lens: focuses light rays. Iris: control the size of the pupil  regulating the amount of light reaching the retina Retina: a layer of receptor cells Receptor cells  rods and cones

ch 316 Retina:

ch 317 Photo receptors are facing away from the light source. The optic nerve carries neural information to this spot. What happens? –No receptors, no vision  blind spot

ch 318 Some messages: how to improve your vision Massage your eye muscles Eat carrots Massage the back of your head.

ch 319 Rods and cones Morphology Distribution on the retina Dark adaptation Spectral sensitivity

ch 320 The distribution of cones and rods on the retina Cones are concentrated mainly on the fovea. There are no rods on the fovea. We move eyes to capture images on the fovea.

ch 321 Demonstration Blind spot

ch 322 Rods and cones are different In their dark adaptation rates

ch 323 Dark adaptation rates of rods and cones When you enter a dark room from outside, you can’t see well at first. But gradually, your eyes are adjusted to the dark, and see better.

ch 324 Review

ch 325 Visual perception What is the difference between (a) & (b)? What is going on in your head when you see (a) versus when you see (b)? (a) (b)

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ch 328 How about this?

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ch 335 What’s going on? When you see the square, what’s going on? How do you find out?

ch 336 In terms of the activity of neurons, what is the difference between A and B ? Any guess? A. B.

ch 337 Measuring the electrical activity of a neuron directly by inserting a thin needle into animal brains.

ch 238 Time 0t The frequency of action potential Time 0 t The number of action potential emitted by a neuron is correlated with the intensity of the stimulus. Time 0 t 5 units 10 units 20 units

ch 2 39 Physical quantities Time 0 t 0 t 5 units 20 units Perceived quantities

ch 340 Neural Processing by Convergence Why are rods more sensitive to light than cones?

ch 341 Activities of neurons can be schematically shown as B a1 a2 a3 a4 The firing rate of neuron B is determined by the activation sent by neurons a1-a4.

ch 342 Ganglion cell

ch 343 Convergence: The ratio of connections with two groups of neurons. Rods vs. Ganglion cells –120:1 Cones vs. Ganglion cells –6:1

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ch 346 Why does this matter? How is this related to the higher sensitivity of rods?

ch 347 The cones result in better detail vision than the rods Visual acuity –How far apart are two dots?

ch 348 Time 0t The frequency of action potential Time 0t 0t The number of action potential emitted by a neuron is correlated with the intensity of the stimulus.

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ch 351 Fig. 2.11, p.53

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ch 355 Demonstration: On a scratch paper, draw two vertical lines of about 2 inches (1/2 inch apart). Close your left eye, and focus your right eye on your index figure, and move the figure. At some point, you can’t distinguish the two vertical lines.

ch 356 The distribution of cones and rods on the retina Cones are concentrated mainly on the fovea. There are no rods on the fovea. We move eyes to capture images on the fovea.

ch 357 Visual Cortex

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ch 360 The cones result in better detail vision than the rods Visual acuity –How far apart are two dots?

ch 361 Neurons How do you detect there are two separate dots (lights)?

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ch 363 How do you detect there are two separate dots (lights)?

ch 364 Rods are bigger than cones Convergence:

ch 365 Lateral Inhibition & Mach bands

ch 366 Herman grid

ch , 10, 10, 10, 10, 10, 10, Physical quantities 10, 5, 10, 5, 10, 5, 10, Perceived quantities  Something is going on inside your brain.  What is it?  Can you explain “something” in terms of the way neurons talk to each other?

ch 368  Something is going on inside your brain.  What is it?  Can you explain “something” in terms of the way neurons talk to each other? Some neurons send excitatory (+) signals (transmitter), and other neurons send inhibitory (-) signals.

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ch 271 Time 0t The frequency of action potential Time 0 t The number of action potential emitted by a neuron is correlated with the intensity of the stimulus. Time 0 t 5 units 10 units 20 units

ch 372 Questions: What happens to B? 0 t

ch 373 Questions: What happens to B? ExcitatoryInhibitory

ch 374 Receptive field The receptive field of a neuron in the visual system is the area on the retina that influences the firing rate (action potential) of the neuron. Measuring the receptive field of a ganglion cell

ch 375 Receptive field of a ganglion cell Measuring the frequency of action potentials elicited by this ganglion cell. Cones Ganglion cell B

ch 376 Receptive field of a ganglion cell Cones Ganglion cell B Firing rate of B

ch 377 Questions: What happens to B?

ch 378 Measuring the receptive field of a ganglion cell Change the size of the stimulus and see the way a ganglion cell respond

ch 379 Cones Ganglion cell B

ch 380 ExcitatoryInhibitory Excitatory- center- inhibitory- surround receptive field

ch 381 Questions: What happens to B? ExcitatoryInhibitory

ch 382 Excitatory and inhibitory connections What neurons transmit is electricity. Some neurons send positive (excitatory) signals (+)  increase the firing rate of the target neuron. some neurons send negative (inhibitory) signals (-)  depress the firing rate of the target neuron.

ch 383 Spatial Summation c1 c2 c3 c4 B a1 a2 a3 a4 + + = B a1 a2 a3 a4 + + = The firing rate of neuron B can be expressed by the overall summation of the signals that B receives.

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ch 386 How does this happen?

ch 387 =sum(B)

ch 388 Fig. 3-6, p. 50

ch 389 Fig. 3-7, p. 51

ch 390 Why is this important?  help you to detect the edge of a figure

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ch 392 Light intensity location Perceived Light intensity location

ch 393 Physical stimuliYour perception

ch 394 Lateral inhibition

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ch 398 White’s illusion Can you explain this by lateral inhibition?

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ch 3106 Application: Machine vision Implementing lateral inhibition into a computer program.

ch 3107 Image

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ch 3111 Edge detection algorithm –Zero-crossing