PSYCH 2220 Sensation & Perception I Lecture 3. Keywords for lecture 2 Air-dwelling eye, water-dwelling eye, (both: mask, powerful lens, flat cornea, pinhole),

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Presentation transcript:

PSYCH 2220 Sensation & Perception I Lecture 3

Keywords for lecture 2 Air-dwelling eye, water-dwelling eye, (both: mask, powerful lens, flat cornea, pinhole), presbyopia, astigmatism, accommodation, depth of focus, ophthalmoscope, retina, retinal blood vessels, fovea, optic disk, blind spot, retina, cells, cell membrane, ions, potassium, sodium, channels (meaning 1), neurones, resting potential (-70mV), action potential, synapse, neurotransmitter, Schwann cells, axon, dendrites, polarization, depolarization, hyperpolarization, dark/light adaptation, rods, thresholds, sensitivity, cones, visual purple, Purkinje shift, scotopic, photopic, fovea, receptive fields, bipolar cells, retinal ganglion cells

Eye movements Point eyes to right place Accommodation focus Pupils Light Adaptation Adjust for the light level Transduction Convert light energy to activity in cells

Optic Disc Fovea

The foveal pit

RETINAL GANGLION CELLS

Bipolar cell CONVERGENCE ….. which means the receptive field of a RGC is bigger than a photoreceptor

Bipolar cell DIVERGENCE ….. which means the receptive fields of RGCs overlap.

Excitatory Bipolar cell Inhibitory Bipolar cell receptive field spontaneous activity

Excitatory Bipolar cell Inhibitory Bipolar cell OFF-CENTRE CELL

Excitatory Bipolar cell Inhibitory Bipolar cell

Excitatory Bipolar cell Inhibitory Bipolar cell ON-CENTRE CELL

VIDEO from disc… Look at how the cells will respond to an edge. Followed by Sustained and Transient

video...

response space response to spot in centre response to spot in surround spontaneous level 0 high low LIGHT DARK

Mach bands

HI !

Types of Retinal Ganglion Cells On-centre Off-surround Off-centre On-surround SustainedtransientSustainedtransient

Perceptual effects that can be understood from knowing about retinal ganglion cells...

Mach bands

Simultaneous contrast

Scallop illusion

Scallop illusion luminance

A light check in the shadow is the same gray as a dark check outside the shadow. ©1995, Edward H. Adelson

PHYSICAL PERCEPTUAL luminancebrightness wavelengthcolour

Hermann Grid

less inhibition

RETINAL GANGLION CELLS Have spontaneous activity show action potentials can be inhibited by light can be excited by light have concentric fields have smaller fields in the fovea (they also respond in an interesting and surprising way to colour, but we’ll come back to that when we look at colour)

INFORMATION GOING TO BRAIN is LIMITED (partial) is ALREADY PROCESSED is in the form of ACTION POTENTIALS is DISTORTED (fovea more) tells about EDGES (change)

Introduction to the structure of the brain

Cortex

Lateral geniculate nucleus of the THALAMUS

Organization of the lateral geniculate of the THALAMUS (1) Parvocellular layers (3- 6) Magnocellular layers (1- 2)

Injection of tracer to left eye

CORTEX

Magnification factor when looking at the centre, each letter uses the same amount of cortex

David HubelTorsten Wiesel Plotting the receptive field of a simple cell…..

Hubel & Wiesel described three types of cells in the cortex: simple complex hypercomplex from their responses all vision is built up. They received a NOBEL PRIZE for this work.

SIMPLE CELLS are orientation tuned...

Complex cells