1 Key terms Psychophysics traditionally the term psychophysics refers to the quantitative methods for measuring the relationship between properties of the stimulus and the subject s experience All methods used to determine the relationship between stimuli and perception are psychophysical methods b Panpsychism The idea that the mind exists as a property of all matter that is that all matter has consciousness c Criterion In signal detection theory an internal threshold that is set by the observer If the internal response is above criterion the observer gives one response e g yes I hear that Below criterion the observer gives another response e g no I hear nothing d cross modal matching The ability to match the intensities of sensations that come from different sensory modalities This ability enables insight into sensory differences For example a listener might adjust the brightness of a light until it matches the loudness of a tone e magnitude estimation A psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli f signal detection thoery a theory stating that the detection of the stimulus depends both on the participant s sensitivity to the stimulus and on the participant s response criterion o The signal is the target stimulus and the noise is the interference that occurs and is sometimes confused with the signal g spatial frequency The number of cycles of a grating per unit of visual angle usually specified in cycles per degree h Phase In vision the relative position of a grating 2 In hearing the relative timing of a sine wave 2 Anatomy of a neuron neurotransmitters neuron axon dendrites receptor myelin ect and basic structure layers of the cortex a Neurons come in all shapes and sizes Let s consider a canonical pyramidal neuron o Dendrites that receive inputs from other neurons often mixture of inhibitory and facilitatory inputs o Cell body that nucleus and mitochondria o Longer axons have myelin sheath that allows rapid and efficient signal conduction o Axon terminal sends signal to next neuron o Important notes All or none conduction time 1m 100ms firing rate refractory period electrochemical gradient a Neurotransmitters A chemical substance used in neuronal communication at synapses b Cortical layers The cortex has a building code Six layers 3mm thick o Surface layers 1 3 connect to other parts of the cortex o Middle layer 4 receives inputs from the thalamus relay from body Very distinct in sensory cortex o Deep layers 5 6 connect to subcortical regions Most distinct in motor regions of the brain 3 Types of nerve cells auditory nerves cranial nerves oculomotor nerves olfactory nerves optic nerves trochlear nerves 4 Weber s law theories Joseph Fourier and Allegory in the cave a The Allegory of the Cave in Plato s Republic depicts our ordinary sense of reality as beings like prisoners in a cave The prisoners are tethered together since childhood bound to face only the wall in front of them and all they are able to see are the shadows on the wall in front of them This is their reality and this depiction is meant to show how much of our conception of reality depends on what we can learn about the world through our senses b Weber observed ability to denote change just noticeable difference JND relative to physical intensity of stimulus a c Joseph Fourier realized that signals can be transformed to sine waves 2 Signal to noise ration and examples a Car radios are a good example of SNR a When we are near the radio transmitter the signal is crisp high SNR b As we drive further away the signal degrades Eventually it becomes hard to understand what the radio announcer is saying poor SNR c Photography is a good example o Our photos have good SNR if the light is bright and we are photographing a static object slow shutter speed o We will compromise SNR if we want to freeze motion fast shutter speed o We will compromise SNR if taking a photo in a dark room need to boost amplification o It is easy to discriminate events if there is high signal to noise but harder if there is a lot of noise o Again think of trying to determine if the phone is ringing when you are in the show Harder to discriminate if the phone is quiet low signal or if the shower is loud high noise Neuroimaging techniques fMRI MEG EEG CT PET a Electroencephalography EEG and magnetoencephalography MEG measure the activity of many neurons with great precision in timing but not brain location b Positron emission tomography PET and functional magnetic resonance imaging fMRI measure metabolic changes to precisely localize the activity of many neurons in the brain but with little precision in timing c computed tomography CT An imaging technology that uses X rays to create images of slices through volumes of material e g the human body Thresholds JND two point touch absolute a Absolute threshold minimum stimulus intensity that can just be detected o minimal amount of stimulation necessary for a person to detect the stimuli 50 of the time o Discrimination between stimuli presence or absence b Two point touch threshold the minimal distance between two tactile stimuli in which they can be distinguished from each other c Just Noticeable Difference threshold the minimal difference between two stimuli that can be correctly distinguished from each other Discrimination between two stimuli o The JND is the smallest detectable difference between two stimuli or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus It is also known as the difference threshold It is a key tool for investigating psychophysiological phenomena 2 Method of adjustment limits constant stimuli a Method of adjustment a method of limits in which the subject controls the change in the stimulus b 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 participants responds differently c Method 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 yes no same different and so on