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Chapter 1-4


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Matthias Niemeier

CHAPTER 1: INTRODUCTION Sensation and Perception - Ability to detect the pressure of a finger, and, perhaps, to turn that detection into a private experience is an example of sensation - Perception can be thought of as the act of giving meaning to those detected sensations - French philosopher Etienne Bonnot de Condillac asked his readers to imagine mental life of a statue with no senses, and concluded that the statue would have no mental life; with more senses and more experience, Condillac imagined a real mental life developing in statue THRESHOLDS AND THE DAWN OF PSYCHOPHYSICS - Gustav Fechner invented psychophysics and is thought to be the true founder of experimental psychology, even if that title is usually given to Wilhem Wundt who began his work a little later - Fechner had a degree in medicine, then turned from biology to physics and math - Fechner suffered eye damage from gazing at the sun too much while performing vision experiments, this led to his depression leaving him alone most of the time with his own thoughts - When his vision recovered he became absorbed with the relationship between mind and matter - This pursuit placed him in the middle of a classic philosophical debate between adherents of dualism and materialism - 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 nits of matter - Fechner suggested panpsychism: the idea that the mind exists as a property of all matter that is, that all matter has consciousness - Fechner described his philosophy of panpsychism in his book called Concerning the Mental Life of Plants - Fechners goal was to formally describe the relation between sensation (mind) and the energy (matter) that gave rise to that sensation - He called his theory psychophysics: the science of defining quantitative relationships between physical and psychological events - Fechner was inspired by the findings of Ernst Weber - Weber used a device to measure the smallest distance between two points that was required for a person to feel two points instead of one - Two-point touch threshold: the minimum distance at which two stimuli are just perceptible as separate - Weber also discovered the just noticeable difference (JND) - JND: 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 - The smallest weight that could be detected was always close to one-fortieth of the standard weight - Weber fraction: the constant proportionality in Webers law - Webers law: the principle describing the relationship between stimulus and resulting sensation that says the just noticeable difference is a constant fraction of the comparison stimulus - Fechners law: a principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity o S = k log R S is the psychological sensation, which is equal to the logarithm of the physical stimulus level (log R) multiplied by a constant, k - Absolute threshold: the minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time Psychophysical Methods - Method of constant stimuli: a psychophysical method in which many stimulus, ranging from rarely to almost always perceivable, are presented one at a time. Participants respond to each presentation: yes/no, same/different, and so on. - Method of constant stimuli can be somewhat inefficient in an experiment because much of the subjects time can be spent with stimuli that are clearly well above or below threshold - 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 There is some overshoot in judgements, meaning it takes more intensity to report hearing the tone when its increasing, and more decreases in intensity before a listener reports the tone cannot be heard - Method of adjustment: a method of limits in which the subject controls the change in the stimulus o This method is not usually used to measure thresholds Scaling Methods and Superstars - Magnitude estimation: a psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli o Works well when observers are free to choose their own range of numbers o Magnitude estimation invented by Harvard psychologist S. S. Stevens - Stevens power law: a principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent o S = aI^b - Webers law involves clear objective measurement - Fechners law begins with the same sort of objective measurements and Webers but the law is actually a calculation based on some assumptions about how sensation works; in particular, Fechners law assumes that all JNDs are equivalent, in fact this turns out to be incorrect and leads to some places where the law is violated - Stevens power law describes rating data quite well, but notice that rating data are qualitatively different from the data that supported Webers law - 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 listen might adjust the brightness of a light until it matches the loudness of a tone. - There is a molecule called propylthiouracil (PROP) that some ppl experience as very bitter, while others experience it as almost tasteless (this is a limitation to cross-modality matching) - Supertasters: an individual whose perception of taste sensations is most intense 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. Measures obtained from a series of presentations are sensitivity (d) and criterion of the observer. o Posits that the stimulus youre trying to detect is always being detected in the presence of noise or internal noise - Internal noise static in your nervous system - External noise generated in the world - Criterion: in SDT, 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). - 4 possible outcomes o Say no when there is no ring correct rejection o Say yes when there is a ring hit o Say yes when there is no ring false alarm o Say no when there is a ring miss - Sensitivity: in SDT, 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. - Changing the criterion level changes the this and false alarms in predictable ways - Receiver operating characteristic (ROC) curve: in studies of signal detection, 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 the signal. As the observers sensitivity increases, the curve bows upward toward the upper left corner. That point represent a perfect ability to distinguish signal from noise Fourier Analysis - Joseph Fourier developed analyses that permit modern perception scientists to better understand how complex sounds such as music and speech, complex head motions, and complex images such as objects and scenes can be decomposed into a set of simpler signals - One of the simplest kinds of sounds is a sine wave - Sine wave: 1. In hearing, a waveform for which variation as a function of time in a sine function. Also called pure tone. 2. In vision, a pattern for which variation in a property like brightness or color 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: 1. In vision, the relative position of a grating. 2. In hearing, the relative timing of a sine wave. - Phase is measured in degrees, with 360 degrees of phase across one period - 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. - Spatial frequency: the number of cycles of a grating per unit of visual angle (usually specified in cycles per degree) - Cycles per degree: the number of pairs of dark and bright bars per
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