VisionVision

Psychology 2606Psychology 2606

Some introductory thoughtsSome introductory thoughts

Sensory world in general is basically a Sensory world in general is basically a representation of the real worldrepresentation of the real world

So, we have a rich visual world, not much So, we have a rich visual world, not much of a smelly oneof a smelly one

Different parts of the brain do different bits Different parts of the brain do different bits of processingof processing

This all comes together basically This all comes together basically seamlessly to form our visual worldseamlessly to form our visual world

VisionVision

Like any sensory process, vision converts Like any sensory process, vision converts some energy to neural messagessome energy to neural messages

In this case, light In this case, light Light is just a form of electromagnetic Light is just a form of electromagnetic

radiationradiationSo are x rays, micro waves, infra red, UV So are x rays, micro waves, infra red, UV

cosmic rays etccosmic rays etc

I wish to hell I could see I wish to hell I could see better….better….

Wavelength of light determines hueWavelength of light determines hue Intensity determines brightnessIntensity determines brightnessLight enters the eye through the cornea Light enters the eye through the cornea

and the pupiland the pupilPupil size regulated by irisPupil size regulated by irisBehind pupil, lens, which accommodatesBehind pupil, lens, which accommodatesLight hits the retinaLight hits the retinaOh ya, it is upside down….Oh ya, it is upside down….

AcuityAcuity

Acuity is affected by Acuity is affected by the shape of the eyethe shape of the eye

Nearsighted, eye too Nearsighted, eye too long, or cornea too long, or cornea too curvedcurved

So far away stuff is So far away stuff is blurryblurry

Image is in front of Image is in front of the retinathe retina

Farsighted, oppositeFarsighted, opposite

The retinaThe retina

There are two kinds of There are two kinds of receptors in the retina, receptors in the retina, rods and conesrods and cones

Rods for night, brightnessRods for night, brightness Cones for day, colourCones for day, colour When a photon hits a When a photon hits a

receptor it sends a receptor it sends a message via the optic message via the optic nerve to the brainnerve to the brain

Because of this, we have Because of this, we have a blind spot!a blind spot!

Gotta love the retinaGotta love the retina

Cones are for fine detail and colourCones are for fine detail and colourCones only really work in the lightCones only really work in the lightConcentrated in the foveaConcentrated in the foveaRods are more evenly distributedRods are more evenly distributedMany rods to one bipolar cell, so you can Many rods to one bipolar cell, so you can

see in dim light, but only in black and whitesee in dim light, but only in black and whiteOne cone, one bipolar cellOne cone, one bipolar cellAbout 130 000 000 receptors per retinaAbout 130 000 000 receptors per retina

Follow the optic nerveFollow the optic nerve

Connection is next to the ganglion cells in Connection is next to the ganglion cells in the optic nervethe optic nerve

Cross at the optic chiasmCross at the optic chiasmLeft visual field to right half of brain, right Left visual field to right half of brain, right

to leftto leftNext the path goes to the LGNNext the path goes to the LGNGeniculostriate systemGeniculostriate systemSome to occipital lobe some to parietalSome to occipital lobe some to parietal

And there is another pathway….And there is another pathway….

Superior colliculus in the tectumSuperior colliculus in the tectumPulvinar in thalamusPulvinar in thalamusWhole thing is called the tectopulvinar Whole thing is called the tectopulvinar

systemsystemMedial pulvinar, parietalMedial pulvinar, parietalLateral pulvinar, temporalLateral pulvinar, temporal

Dorsal and ventral streamsDorsal and ventral streams

Temporal -> ventralTemporal -> ventralParietal -> dorsalParietal -> dorsal

Occipital lobeOccipital lobe

V1 – V5V1 – V5Blobs and interblobs in V1Blobs and interblobs in V1Blobs do colour, interblobs do motion and Blobs do colour, interblobs do motion and

formform Info goes on to V2Info goes on to V2Now the dorsal and ventral streams are Now the dorsal and ventral streams are

producedproduced

Receptive FieldsReceptive Fields

The region of the retina that when stimulated will The region of the retina that when stimulated will cause a cell to firecause a cell to fire

This is coded on to layers in V1This is coded on to layers in V1 So top is top layer, etcSo top is top layer, etc Cortical cells have receptive fields tooCortical cells have receptive fields too Receptive field in cortex relates to much bigger Receptive field in cortex relates to much bigger

area that receptive field in retina, so , many area that receptive field in retina, so , many ganglion cellsganglion cells

Only adjacent areas of visual field in centre have Only adjacent areas of visual field in centre have colossal connectionscolossal connections

So, for example, we can see shape by the So, for example, we can see shape by the nervous system analyzing luminance nervous system analyzing luminance contrast between receptive fieldscontrast between receptive fields

Simple cells, orientationSimple cells, orientationComplex cells, orientation and movementComplex cells, orientation and movementHypercomplex cells, orientation, Hypercomplex cells, orientation,

movement and inhibition on one sidemovement and inhibition on one side

V1 – V5V1 – V5

V1 and V2 are basically like V1 and V2 are basically like clearinghouses into which different bits of clearinghouses into which different bits of information are deposited and then routed, information are deposited and then routed, post offices if you willpost offices if you will

Connections from blobs in V1 to V4 (so V4 Connections from blobs in V1 to V4 (so V4 does some things with colour)does some things with colour)

V4 does some stuff about form tooV4 does some stuff about form tooV5 only does motionV5 only does motionV3 does ‘dynamic form’ (shape in motion)V3 does ‘dynamic form’ (shape in motion)

V was a bad early 80s sci fi showV was a bad early 80s sci fi show

Damage to V4 -> only see shades of greyDamage to V4 -> only see shades of greyDamage to V5 -> motion detection is goneDamage to V5 -> motion detection is goneV1 damage, blind, yet they can see!V1 damage, blind, yet they can see!So V1 probably is where the brain makes So V1 probably is where the brain makes

sense of visual inputsense of visual input

Case studies can be usefulCase studies can be useful

DB -> V1 Damage and blindsightDB -> V1 Damage and blindsightJL -> V4 Damage and colourJL -> V4 Damage and colourLM -> V5 Damage and movement LM -> V5 Damage and movement

perceptionperceptionDF -> General occipital damage and visual DF -> General occipital damage and visual

agnosiaagnosiaD and T -> Higher level visual processingD and T -> Higher level visual processing

ConclusionsConclusions

Visual system is way complexVisual system is way complex It is, frankly, counter intuitiveIt is, frankly, counter intuitive It is not all occipitalIt is not all occipitalVision is clearly important to humans, as Vision is clearly important to humans, as

much of our brain is devoted to itmuch of our brain is devoted to itThere MAY be asymmetriesThere MAY be asymmetries