• Sensation: the ability to detect a stimulus and, perhaps, to turn that detection into a private experience
  • Perception: the act of giving meaning to a detected sensation
  • Condillac: mental life relies on information from our senses

Methods used in the study of the senses

  • Thresholds
  • Scaling: measuring private experience o Quale: in philosophy, a private conscious experience of sensation or perception
  • Signal detection theory – measuring difficult decisions
  • Sensory neuroscience
  • Neuroimaging – an image of the mind

Thresholds and the dawn of psychophysics

  • Dualism: the idea that the mind has an existence separate from the material world of the body
  • Materialism: the idea that the only thing that exists is matter, and that all things, including the mind and consciousness, are the results of interactions between bits of matter
  • Panpsychism: the idea that the mind exist as a property of all matter, that is, that all matter has consciousness (Fechner)
  • Psychophysics: the science of defining quantitative relationships between physical and psychological (subjective) events (Fechner)
  • Two-point touch threshold: the minimum distance at which two stimuli are just perceptible as separate (Weber)
  • Just noticeable difference/ difference threshold: the smallest detectable difference between two stimuli, or the minimum change in a stimulus that enables it to be correctly judged as different from a reference stimulus (Weber)
  • Weber’s law: the principle describing the relationship between stimulus and resulting sensation that says the JND is a constant fraction of the comparison stimulus (e.g. 1:100 for length, 1:40 for weight) o Clear objective measurement, we know how much the stimulus varied and the observer can either tell that it changed or not
  • Fechner’s law: a principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation(S) increases proportionally to the logarithm of the stimulus intensity(R) (S = k log R) o Describes the relationship between mind and matter
    • The smallest detectable change in a stimulus can be considered as a unit of the mind, because this is the smallest bit of change that is perceived
    • Assumes that all JNDs are perceptually equivalent, which turns out to be incorrect
  • Absolute threshold: the min amount of a stimulation necessary for a person to detect a stimulus 50% of the time

Detected 50% of the time due to the variability in the nervous system, stimuli near the threshold will be detected sometimes and missed other times → there is no hard boundary

Psychophysical methods

  • Method of constant stimuli: a psychophysical method in which many stimuli ranging from rarely to almost always perceivable, are presented one at a time and participants respond to each presentation: yes/no 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 o Tones are presented in increasing or decreasing intensity; increasing: report when you first hear the tone; decreasing: report when the tone is no longer heard. The threshold is set at the average of the crossover points
  • Method of adjustment: a method of limits in which the participant controls the change in the stimulus

Scaling methods and supertasters

  • Magnitude estimation: a psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli o Steven’s power law: a principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation(S) is proportional to the stimulus magnitude(I) raised to an exponent(b) ( S = aIb )
  • Measures subjective ratings, and we can check whether these are reasonable and consistent but there is no way of knowing whether they are objectively right or wrong
  • Cross-modality 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, the relationship between modalities appears to be similar across individuals

Signal detection theory

  • Signal detection theory: a psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise (internal noise, the static in your nervous system). Measures obtained from a series of presentations are sensitivity (d’) and criterion of the observer o Criterion: an internal threshold set by the observer. If the internal response is above the criterion, the observer gives one response (yes) and below the criterion the observer gives another response (no)
  • Correct rejection, hit, false alarm, miss o Sensitivity: a value that defines the ease with which an observer can tell the difference between the presence and absence of a stimulus or the difference between stimulus 1 and stimulus 2 (d’ or d-prime)

Receiver operating characteristic (ROC) curve: the graphical plot of the hit rate as a function of the false-alarm rate. If these are the same, points fall on the diagonal, indicating that the observer cannot tell the difference between the presence and absence of a signal. As the observer’s sensitivity increases, the curve bows upward toward the left corner, that point represents the perfect ability to distinguish signal from noise (100% hits, 0% false alarms). Figure 1.14 page 14

Fourier analysis

  • Sine wave:
    • In hearing: a pure tone: a waveform for which variation as a function of time is a sine function
    • In vision: a pattern for which variation in a property like brightness or colour as a function of space is a sine function
  • Period or wavelength: the time (or space) required for one cycle of a repeating waveform
  • Phase: the relative position to a fixed marker o In hearing: the relative time of a sine wave o In vision: the relative position of a grating
  • Fourier analysis: a mathematical procedure by which any signal can be separated into component sine waves at different frequencies. Combining these sine waves will reproduce the original signal o Sounds: changes in pressure across time
    • Spatial frequencies: images can be broken down into components that capture how often changes from light to dark occur over a particular region in space, spatial frequencies are defined as the number of these light/dark changes across one degree of a person’s visual field
    • Cycles per degree: the number of pairs of dark and bright bars per degree of visual angle

Sensory neuroscience and the biology of perception

  • Doctrine of specific nerve energies: states that the nature of sensation depends on which sensory fibres are stimulated, not on how fibres are stimulated (Müller) o We are only aware of the activity of our nerves, we cannot be directly aware of the world itself -Cranial nerves:
    • Olfactory (I): smell → sensory o Optic (II): vision → sensory o Oculomotor (III): all eye muscles except superior oblique and lateral rectus → motor o Trochlear (IV): superior oblique muscle → motor o Trigeminal (V): face, sinuses, teeth → sensory and motor o Abducens (VI): lateral rectus muscle → motor o Facial (VII): tongue, soft palate → sensory and motor o Vestibulocochlear (VIII): spatial orientation, balance, hearing → sensory o Glossopharyngeal (IX): posterior tongue, tonsils, pharynx, pharyngeal muscles → sensory and motor

Vagus (X): heart, lungs, gastrointestinal tract, bronchi, tranchea, larynx → sensory and motor

  • Spinal accessory (XI): sternomastoid and trapezius muscles → motor o Hypoglossal (XII): tongue muscles → motor
  • Polysensory: as processing extends beyond primary areas, information of more than one sense is being combined in some matter
  • Vitalism: the idea that there is a force in life that is distinct from physical entities (Müller) o Helmholtz: all behaviour should be explained by only physical forces: the activity of neurons obeys normal rules of physics and chemistry, the speed with which neurons transmit their signals can be measured

Neural connections

  • Synapse (Cajal, Sherrington)
  • Exhibitory versus inhibitory activity → chemical instead of electrical in the synapse (Loewi)
  • Neural firing is electrochemical: voltage increases along the axon are caused by changes in the membrane of the neuron that permit positively charged sodium ions (Na+) to rush very quickly into the axon from outside. Then the membrane very quickly changes again in a way that pushes positively charged potassium ion (K+) outside the axon, restoring the neuron to its initial resting voltage (Hodgkin and Huxley)

Neural firing: populations of neurons

  • CT scan (Computerized Tomography): a narrow beam of x-rays creates a series of brain slices → static image
  • PET scan (Positron Emission Tomography): radioactive tracers are injected into the blood stream together with glucose, radioactive glucose goes to specific brain regions due to several activities.
  • fMRI (functional Magnetic Resonance Imaging): magnetic fields are used to track the iron in blood, to monitor increases in blood flow to the brain.
    • BOLD: blood oxygen level-dependent
  • MEG (MagnetoEncephaloGraphy): just as fMRI but with time frame