Today: finish w/ Human BrainBrain; and then SensorsSensors & PerceptionPerception

During an infant’s or child’s brain development, …

While working with their hands, most right-handed peopleright-handed people use the left hand (right hemisphere) for context or holding and use the right hand (left hemisphere) for fine detailed movement.

The leftleft hemisphere is most adept at language, math, logic operations,serial sequences of information,

detailed, speed-optimized activities, fine visual and auditory details.

focused perception.

{the ‘reductionist hemisphere’}

The rightright hemisphere is stronger at pattern recognition, face recognition, spatial relations, nonverbal ideation, emotional processing in general, music; perception of the relationship between images and the whole context in which they occur.{the ‘holostic hemisphere’}

The left hemisphere's role in hypothesis formation.Wolford G et al. 2000. Journal of Neuroscience 20: RC64

Abstract:In a probability guessing experiment, subjects try to guess which of two events will occur next. Humans tend to match the frequency of previous occurrences in their guesses. Animals other than humans tend to maximize or always choose the option that has occurred the most frequently in the past. Investigators have argued that frequency matching results from the attempt of humans to find patterns in sequences of events even when told the sequences are random.

There is independent evidence that the left hemisphere of humans houses a cognitive mechanism that tries to make sense of past occurrences.We performed a probability guessing experiment with two split-brain patients and found that they approximated frequency matching in their left hemispheres and approached maximizing in their right hemispheres. We obtained a conceptual replication of that finding on patients with unilateral damage to either the left or right hemisphere. We conclude that the neural processes responsible for searching for patterns in events are housed in the left hemisphere.

http://www.bio.psy.ruhr-uni-bochum.de/asymhumans.htm

We use different methods to investigate functional cerebral asymmetries …One of them is the visual half-field techniquethe visual half-field technique in which stimuli (faces, words, figures, illusory figures) are presented for 180 ms in the left or the right visual field of a person which fixates a cross in the middle of a computer screen. {180ms is too brief to shift eyes}Due to the pattern of projections within the human visual system, stimuli shown on the right are represented in the left hemisphere and vice versa. If words are shown on the right side (left hemisphere), reaction times are faster and percent correct measures are higher due to the language-dominance of the left hemisphere. The opposite is true for faces and abstract figures (Hausmann and Güntürkün, 1999).

The ability to observe which structures participate in specific functions is due to a new technique called functional magnetic resonance imaging, fMRI: functional magnetic resonance imaging, fMRI: provides high resolution, noninvasive reports of neural activity detected by a blood oxygen level dependent signal … This new ability to directly observe brain function {blood flow} opens an array of new opportunities to advance our understanding of brain organization … to mental operations … maps of human brain function.

http://www.alumni.berkeley.edu/Alumni/Cal_Monthly/September_2001/Making_up_your_mind.asp

Functional MRI of a volunteer committing a list of words to memory. The colored spots represent increased blood flow and brain activity. The circled region is a part of the frontal cortex where activity was higher for words that were later remembered than for words that were later forgotten.

The hippocampus, amygdala, some inner portions of the cortex’s lobes and sections of the thalamus and hypothalamus, form a ring around the brainstem called the limbic system: the limbic system: - interacts with neocortex & generates emotionsemotions.

AmygdalaAmygdala activity related to enhanced memory for pleasant and aversive stimuliHamann et al. 1999 Nature Neurosci 2, 289-293. Pleasant or aversive events are better remembered than neutral events. Using positron emission tomography, {PET not fMRI}we show that bilateral amygdala activity during memory encoding is correlated with enhanced episodic recognition memory … The human amygdala seems to modulate the strength of conscious memory for events according to emotional importance …

Maps of pixels in which individual subject rCBF was significantly correlated withindividual-subject episodic-memory enhancement

This is still controversial

ReductionistReductionist efforts are getting us to the neural correlates of brain function,

But we still haven’t found ‘the mind.’

http://socrates.berkeley.edu/~jsearle/html/consciousness.html

… the neurobiological problem of consciousnessconsciousness is this:

How exactly do brain processes cause conscious states How exactly do brain processes cause conscious states and how exactly are those states realized in brain structures?and how exactly are those states realized in brain structures?

Consciousness. Searle JR. Annual Review of Neuroscience 23: 557-578 2000.Some relevant research on consciousness involves the subjects of blindsight, the split-brain experiments, binocular rivalry, and gestalt switching.

{Fig. 48.24a}

The picture is flashed faster than eye scan;

http://www.sciamarchive.org/pdfs/635348.pdf

Later: illusions & alt. hypotheses

Cerebral specialization and interhemispheric communication - Does the corpus callosum enable the human condition?Gazzaniga MS 2000 BRAIN 123:1293-1326.

http://socrates.berkeley.edu/~jsearle/html/consciousness.html

BlindsightBlindsight is the name given … to the phenomenon whereby certain patients with damage to V1 {visual cortex} can report incidents occurring in their visual field even though they report no visual awareness of the stimulus.

{Our consciousness is just the tip of a cognitive iceberg! }

For example, in the case of DB, the earliest patient studied, if an X or an O were shown on a screen in that portion of DB's visual field where he was blind, the patient when asked what he saw, would deny that he saw anything.

But if asked to guess, he would guess correctly that it was an X or an O. His guesses were right nearly all the time. … the subjects in these experiments are usually surprised at their results. When the experimenter asked DB in an interview after one experiment, "Did you know how well you had done?", DB answered, "No, I didn't, because I couldn't see anything. I couldn't see a darn thing." (Weiskrantz 1986: 24).

Neural correlates of conscious self-regulation of emotion.Neural correlates of conscious self-regulation of emotion.Beauregard et al. 2001. Journal if Neuroscience 21 (18):U11-U16.

Abstract:… brain activation was measured {fMRI} in normal male subjects while they either responded in a normal manner to erotic film excerpts { ! } or voluntarily attempted to inhibit the sexual arousal induced by erotic stimuli.

… the sexual arousal experienced in response to the erotic film excerpts, was associated with activation in "limbic" and paralimbic structures, such as the right amygdala {A}, right anterior temporal pole {B}, and hypothalamus {C}.

… the attempted inhibition of the sexual arousal … was associated with activation of the right superior frontal gyrus {A} and right anterior cingulate gyrus {B}. … reinforce the view that emotional self-regulation is normally implemented by … various prefrontal regions …

… … humans have the capacity humans have the capacity to influence the electrochemical dynamics of their brains, to influence the electrochemical dynamics of their brains, by voluntarily changing the nature of the mind processes by voluntarily changing the nature of the mind processes unfolding in the psychological space. unfolding in the psychological space.

There is, however, an increasing consensus that the main reason why humans have so much brainpower is to provide for social intelligence. why humans have so much brainpower is to provide for social intelligence. The human way of life, at least for the last million years, has depended to an unprecedented degree on everyone being part of a complex social network of family and friends. … to succeed in this game of what amounts to "social chess," each individual has always had to be a natural psychologist capable of reading the minds of other humans, reading the minds of other humans, and calculating how they might act nextand calculating how they might act next {empathy & false beliefs test} (and doing this better than the next person).

We don’t know much about the mechanismmechanism of consciousness but there are some interesting guesses about the functionfunction (what selects for it)

http://www.feedmag.com/brain/parts/humphrey.htmlThe brainThe brain may be Woody Allen's second favorite organ,Woody Allen's second favorite organ, but it's the one for which, it seems, size really does matter. The brain of humans is more than three times the size of that of our nearest relatives, the chimpanzees, having swelled from 400 to 1350 cubic centimeters in the last three million years of evolution. …

Older children say that she will look in the basket, because although they know the marble is in the box, they know that Sally doesn't know it has been moved from the basket, and they can distinguish Sally's (false) belief from their own (true) belief. Younger children, and autistic children, simply say that Sally will look in the box. The false belief test, therefore, explores the change that happens as common-sense psychology develops.

Baron-Cohen et al.'s(1996) false belief testfalse belief test is presented as a simple story. 1. There are two puppets, Sally and Anne. Sally has a marble, which she keeps in a basket. 2. Then Sally leaves the room, and while she is away 3. Anne takes the marble out of the basket and hides it in the box. 4. Sally comes back into the room. The child subject is then asked the question: “Where will Sally look for her marble?"

http://pubpages.unh.edu/~jel/seminar/Frith_mind.pdf

Lock Lie

Chapter 49: SENSORY AND MOTOR MECHANISMS

All animals are in constant motion, actively probing the environment with that motion, actively sensing the changes that result, and then using the information to generate the next action.

Sensations begin as different forms of energy such as light, heat, sound, and smells are detected by specialized sensory receptor cells and ultimately converted to action potentials that travel to the brain.Most sensory receptors are specialized neurons or epithelial cells. In most vertebrates, sensory signals generally go first to the thalamus the gateway to the cerebral cortex.

This gateway is influenced by instructions coming back from the cortex. The information is then sent on to the many parts of the brain that contribute to forming our perceptions, our awareness and interpretation of the stimuli.

Limbic regions {emotions} are central in determining the importance of the sensory input to the organism. Our memories … can strongly influence our final perceptions, so that in some cases we perceive what we expect to hear or see …Perception is a very complex result that can be biased by our history ... {perception is active interpretation & sometimes misinterpretation!}

Placebo and opioid analgesia - Imaging a shared neuronal networkPetrovic Pet al. SCIENCE 295 (5560): 1737-1740 MAR 1 2002It has been suggested that placebo analgesia involves both higher order cognitive networks and endogenous opioid systems.

Higher cortical systems may exert direct control over the analgesic systems of the thalamus & brainstem not only during opioid analgesia but also during placebo analgesia

• PET scans in the pain condition showed increased activity in the thalamus (Fig 1A left) and in the caudal anterior cingulate cortex (ACC) (Fig 1A right)•The opioid agonist remifentanil activated the ACC cerebral opioid receptor binding area (1B).•Subjects rated the pain intensity lower during POP (Pain-Opoid) compared with P (Pain only).•The insula of the thalamus (involved in pain processing) had an attenuated response (measured: rCBF=regional Cortical Blood Flow) during POP (1B) as compared with P (1A right).

•Increased activity in the same area of the cortex was also seen in the placebo effect (Fig 1C).

Pain P

Pain+OPiod POP Pain+Placebo PPL

Amplification of the signal may occur in accessory structures like external ears, or be a part of the transduction process itself. An action potential from the eye to the brain has about 100,000 times as much energy as the few photons of light that triggered it.

The detection of a stimulus involves the conversion of stimulus energy into a change in the membrane potential of a receptor cell, a process called sensory transduction. In some cases pressure can stretch the membrane and increase ion flow. In other cases, specific receptor molecules on the membrane of a receptor cell open or close gates to ion channels.

TransmissionTransmission to the CNS; often topographically mapped.

Integration: from sensory adaptation (to no change) summation of EPSPs & IPSPs, lateral inhibition, …

http://www.chemistry.wustl.edu/EduDev/LabTutorials/Vision/Vision.html

1. Rays of light (blue) reflected off of an image {3D} are focused through the lens onto the back of the eye, forming an upside-down image {2D} on the retina. 2. … we can think of the image as a {2D} pixellate map of activated and nonactivated photocells on the retina. 3. A nerve (gold) from each photocell connects to a particular location in the visual cortex of the brain. 4. The brain … reconstructs the pixellate map.

5. The brainThe brain then

interprets interprets the the {2D} pixellate map as an pixellate map as an {3D} imageimage.

So - let’s get to the nuts & bolts of sensory systems - visionsensory systems - vision

So, why do people often need reading glasses when they get older?

The mammalian lens has to be pulled into a more spherical shape by ciliary muscles to shorten the focal length and focus on (‘accommodate’accommodate’) close objects.

& short wavelength Blue long wavelength Red

have slightly different focal lengths

Amacrine & Horizontal cells:lateral inhibition

enhances edges & contrast

In the human retina, rods absent from the fovea. You cannot see a dim star at night by looking at it directly; you can see it at an angle by focusing the starlight onto the periphery & rods. You achieve your sharpest daylight vision by looking straight at the object of interest because cones are most dense at the fovea, (about 150,000 per mm2).

We allocate visual attention bysequentially pointing the fovea(saccades)

‘blind spot’where optic nervepasses through

the retina

Your mind fills the blind spot, and it fills the blind time during eye movements.

It also interprets world as stable if image moves as expected after eye movements.

Edge enhancement from lateral inhibition by amacrine & horizontal cells in retinacreates Mach bandsMach bands

rods peak at 498

Human retinal absorption spectra

longer wavelengthhigher frequency

Electromagnetic spectrum

Honey bees see Ultraviolet but not far red

Pit viper pits detect Infrared

Most fishes, amphibians, reptiles, and birds have strong color vision, but humans and other primates are among the minority of mammals with this ability.

http://www.uwsp.edu/psych/dog/dvision.htmFigure 1 is a rough guesstimate of what a dog and human might see when viewing a color band (the electromagnetic spectrum).Dogs are red-green color blind (occurs in 4% of male humans). Simply put, this is due to having only 2 cone types rather than 3.

HumanHuman ColorColor VisionVision

The trichromatic theory trichromatic theory operates at the receptor level

rods peak at 498

People with normal color vision should see an 8 on the left and a 5 on the right. People with red-green color blindness may see 3 on the left 2 on the right.

The genes for the red and green pigments are both on the X chromosome, quite close to one another, and because men have only one X chromosome, they are more likely to be missing one gene; approximately 2% of men are red-green colorblind.Mutations in blue cone pigment genes are unusual: this gene is on chromosome 7, so everyone has two copies and both would have to be defective in order for a problem to occur.

HumanHuman ColorColor VisionVision

The opponent processes theoryopponent processes theory applies to the neural level of color vision processing.

one does not seeone does not see reddish greens or yellowish blues. We do seeWe do see yellowish greens, bluish reds, yellowish reds etc.

rods peak at 498

cones

ganglion cells

perception

When the 3D world is projected onto the 2D retina, the image is ‘underdetermined:’ different hypothetical ‘real worlds’ could have created the same 2D image.

From phylogeny and ontogeny,

the mind has expectations the mind has expectations (constraint assumptions)(constraint assumptions) about how the real world worksabout how the real world works, things like: every mark is in only one place at a time a dot on one retina corresponds to only one dot on the other matter is smooth and cohesive, etc

We are constantly testing alternative hypotheses against sensory data in “the mind’s eye.”

the correspondence problem{consider clues … }

Necker cube

"Whilst part of what we perceive comes through our senses from the object before us, another part (and it may be the larger part) always comes out of our own mind." William James

http://www.illusionworks.com/html/jump_page.html

The Moon Illusion Explained http://facstaff.uww.edu/mccreadd/introduction.html