PSYB51 FINAL NOTES 1-8!
Early Philosophy of Perception!
!• Plato: Our understanding of reality is restricted to things that we can perceive !
!• Heraclitus: Idea that perceiver cannot perceive the same event in exactly the sam a manner each time !
!• Adaptation: A reduction in response caused by prior or continuing stimulation !
!• Democritus: The world is made up of atoms that collide with one another. Sensations are caused by !
!atoms leaving objects and making contact with our sense organs. Perception is the result of the physical
!interaction between the world and our bodies !
!• Sensory transducer: A receptor that converts physical energy from the environment into neural activity !
Nativism and Empiricism!
!• Nativism: The idea that the mind produces ideas that are not derived from external sources !
!!• Plato: truest sense of reality comes from people’s minds and souls !
!• Descartes’ dualist view of the world: both mind and body exist !
!• Mind-body dualism: the idea positing the existence of two distinct principles of being in the universe: !
!spirit/soul and matter/body !
!• Monism: The idea that the mind and matter are formed from, or reducible to, a single ultimate substance
!or principle of being !
!• Materialism: The idea that physical matter is the only reality and everything including the mind can be
!explained in terms of matter and physical phenomena. Materialism is a type of monism !
!• Empiricism: The idea that experience from the senses is the only source of knowledge !
!• Hobbes: believed that everything that ever be known or even imagined had to be learned through the
!senses, i.e. empiricism !
!• Locke: sought to explain how all thoughts, even complex ones, could be constructed from experience
!with a collection of sensations, i.e. empiricism !
The Dawn of Psychophysics!
!• Fechner: invented “psychophysics” thought to be the true founder of experimental psychology!
!• Panpsychism: The idea that all matter has consciousness (Fechner)!
!• Psychophysics: The science of deﬁning quantitative relationships between physical and psychological
!(subjective) events !
!• Weber: was interested in the smallest difference/change in a stimulus that can be detected !
!• JND: Just noticeable difference, the smallest detectable difference between two stimuli, or the minimum
!change in a stimulus that can correctly judged as different from a reference stimulus. Also known as !
!difference threshold !
!• Example: two-point threshold: The minimum distance at which two stimuli (e.g. two simultaneous !
!touches) can be distinguished !
!• Weber discovered that the JND is a constant proportion of the stimulus level - “Weber’s Law”!
!• Fechner’s Law: A principle describing the relationship between stimulus magnitude and resulting !
!sensation magnitude such that the magnitude of subjective sensation increases proportionally to the !
!logarithm of the stimulus intensity !
!• Stevens’ Power Law: A principle describing the relationship between stimulus magnitude and resulting
!sensation magnitude, such that the magnitude of subjective sensation is proportional to the stimulus !
!magnitude raised to an exponent !
!• Absolute threshold: Minimum amount of stimulation necessary for a person to detect a stimulus 50% of
!the time !
!• Psychophysical Methods: Method of constant stimuli, Method of limits, Method of adjustment, !
!Magnitude of estimation, and Cross-modality matching!
Magnitude of constant stimuli!
!• A psychophysical method in which many stimuli ranging from rarely to almost always perceivable (or !
!rarely to almost always perceivably different from a reference stimulus), are presented one at a time. !
!Participants respond to each presentation y/n or same/different !
Method of Limits!
!• A psychophysical method in which the particular dimension of a stimulus, or the difference between two
!stimuli, is varied incrementally until the participant responds differently !
Method of Adjustment!
!• A method of limits in which the subject controls the change in the stimulus !
!• Participants are asked to assign values according to perceived magnitudes of stimuli!
Cross-modality matching method!
!• Matching intensities/magnitudes of sensations that come from different modalities !
Signal Detection Theory!
!• A psychophysical theory that quantiﬁes the response of an observer to the presentation of a signal in the
!presence of a noise!
!• The shower-and-the-phone situation !
!• There is internal noise and external noise!
!• What inﬂuences biases? cost of decisions, probability of events, personality !
Biology of Perception!
!• Doctrine of speciﬁc nerve endings: a doctrine stating that the nature of a sensation depends on which
!sensory ﬁbres are stimulated, not on how ﬁbres are stimulated !
!• Vitalism: belief that special “vital forces” drive living organisms !
!• Cranial nerves: Twelve pairs of nerves that originate in the brain stem and reach the periphery through
!openings in the skull: Olfactory, optic, oculomotor, trochlear, abducens, auditory !
!• Helmholtz: studied activity of neurons; how fast they transmit signals. Slow speed contradicted vitalism.
!Resonators and ophthalmoscope. Perception as inference !
!• Synapse: the junction between neurons that permit information transfer. Discovered by Santiago Ramon
!y Cajal. Slows down neural signals !
!• Neurotransmitter: a chemical substance used in neural transmission communication at synapses !
!• Neurons ﬁre in all or none fashion for each spike, and the number of spikes per second indicated how !
!excited the neurons is !
!• Each action potential starts near the cell body of a neurone and propagates down the axon towards the
!axon terminal !
!!•"Hodgkin-Huxley cycle: electrochemical process involving Na+ and K+ ions moving in and out of
!!the neuron !
!• Entire populations of neurons work in concert to process information !
!• Electroencephalography (EEG): A technique that, using many electrodes on the scalp, measures !
!electrical activity from populations of many neurons in the brain; often averaged into event-related !
!potentials (ERPs), i.e. voltages are calculated aligned in time relative to the onset of a stimulus (or a motor
!• Magnetoencephalography (MEG): A technique, similar to EEG, that measures changes in magnetic !
!activity across populations of many neurone in the brain !
!• Functional MRI (fMRI): measures localized patterns of activity in the brain through the blood oxygen !
!level-dependent (BOLD) signal!
LECTURE 2 !
A Little Light Physics!
!• Light: a wave, a stream of photons, tiny particles that each consist of one quantum of energy !
!• Light can be absorbed, diffracted, reﬂected, transmitted, or refracted !
!• Absorbed: energy (e.g. light) that is taken up, transformed to other forms of energy !
!• Transmitted: convey light from one place to another through a transparent medium !
!• Reﬂected: energy that is redirected when it strikes a surface !
!• Diffracted: bent, or having waves that are spread out, (e.g. waves of sound or light, as they encounter
!an obstacle, e.g. pass through a narrow aperture)!
!• Refracted: energy that is altered as it passes into another medium (e.g. light entering water from the air)!
!• Refraction is necessary to focus light rays. This is done by the four optical components (cornea, lens, and
!• The ciliary muscles change the shape of the lens, and thus alter its refractive power: accommodation !
!• Using the ophthalmoscope, you can view the back surface of person’s eye: fundus !
Retinal Information Processing!
!• Photoreceptors: cells in the retina that initially transduce light energy into neural energy. Duplex retinas:!
!• Rods: photoreceptors that are specialized for night = scotopic vision !
!• Cones: photoreceptors that are specialized for daylight = photopic vision, ﬁne visa acuity and colour !
!• Some animals have mostly rod retinas or only cones !
!• 3rd photoreceptor for circadian rhythm !
!• Visual pigments are molecules with two parts:!
!!• Chromophore (captures photons)!
!!• Opsin (absorbs light of a speciﬁc wavelength)!
!• 2 types of visual pigments:!
!!• Rhodopsin for rods!
!!• 3 subtypes for 3 cones: S cones (blue light), M cones (green light), L cones (red light)!
!• Capturing a photon: when light hits a photoreceptor, the process of photoactivation begins: ! !
!hyperpolarization and graded potentials (instead of depolarization and action potentials)!
!• Lateral pathway: various regions of the retina interact via lateral inhibition: horizontal cells and !
!amacrine cells !
!• Vertical pathway: photoreceptors to bipolar cells to ganglion cells !
!• A variety of bipolar cells, for instance:!
!!• Diffuse bipolar cells: receive input from multiple photoreceptors (rods and peripheral cones)!
!!• Midget bipolar cells: receive input from a single cone in the fovea (cones connect to two bipolar
!• P cells vs. M cells:!
!!• sustained/transient responses!
!!• sensitive/insensitive to colour!
!!• smaller/larger receptive ﬁelds !
!!• ﬁne/coarser spatial resolution !
!• Receptive ﬁeld: the region in space in which stimuli will activate a neuron !
!• Kufﬂer mapped out the receptive ﬁelds of individuals retinal ganglion cells in the cat and found that !
!ganglion cells have a concentric receptive ﬁeld (ON-center ganglion cell or OFF-center) !
!• Ganglion cells function as ﬁlters tuned to spots of a particular size !
!• They are particularly sensitive to differences in light intensity - contrast. They are less interested in !
!ambient light intensity. Lateral inhibition through lateral pathway !
!• Example: Mach bands with exaggerated edges !
Whistling in the Dark: Dark and Light Adaptations!
!• 5 mechanisms important for dark and light adaptations: pupil dilation, photoreceptors, photopigment !
!replacement, adaptive circuitry, and a neural circuitry of the retina that ﬁlters out contrast information and
!ignores absolute luminance levels !
The dawn of psychophysics: plato: our understanding of reality is restricted to things that we can perceive , heraclitus: idea that perceiver cannot perceive the same event in exactly the sam a manner each time ! Adaptation: a reduction in response caused by prior or continuing stimulation : democritus: the world is made up of atoms that collide with one another. Sensations are caused by ! atoms leaving objects and making contact with our sense organs. Perception is the result of the physical interaction between the world and our bodies ! Sensory transducer: a receptor that converts physical energy from the environment into neural activity : plato: truest sense of reality comes from people"s minds and souls ! Nativism: the idea that the mind produces ideas that are not derived from external sources : descartes" dualist view of the world: both mind and body exist !