Chapter 1 Psychology

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  • Topic: Visual system, Eye, Photoreceptor cell
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  • Published : May 15, 2013
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I. Our Senses Encode the Information Our Brains Perceive
* Synesthesia- The perceptual experience of one sense that is evoked by another sense * For many years scientists dismissed synesthesia as rare curiosity or outright faking * Far more common than previously believed

* Brain regions for different sensory modalities cross-activate one another * Sensation- Simple stimulation of a sense organ
* Perception- The organization, identification, and interpretation of a sensation in order to form a mental representation * Transduction- What takes place when many sensors in the body convert physical signals from the environment into encoded neural signals sent to the central nervous system i. Psychophysics

Psychophysics- Methods that measure the strength of a stimulus and the observer’s sensitivity to that stimulus Gustav Fechner
* ii. Measuring Thresholds
* Absolute threshold- The minimal intensity needed to just barely detect a stimulus A threshold is a boundary
Boundary between two psychological states
Human perceptual system excels at detecting changes in stimulation rather than the simple onset or offset of stimulation Just noticeable difference (JND)- The minimal change in a stimulus that can just barely be detected If a light is bright, it will take a much larger increment to detect the difference and make the JND larger JND can be calculated for each sense

It is roughly proportional to the magnitude of the standard stimulus Weber’s law- The just noticeable difference of a stimulus is a constant proportion despite variations in intensity Ernst Weber- noticed the relationship between the JND and the magnitude of the standard stimulus When calculating a difference threshold, it is the proportion between stimuli that is important; the measured size of the difference, whether in brightness, loudness, or weight, is irrelevant iii. Signal Detection

A lot of other stimuli get in the way of sensing just one stimulus Signal detection theory- An observation that the response to a stimulus depends both on a person’s sensitivity to the stimulus in the presence of noise and on a person’s response criterion Proposes a way to measure perceptual sensitivity; how effectively the perceptual system represents sensory events- separately from the observer’s decision-making strategy Hits, misses, false alarms, and correct rejections

iv. Sensory Adaptation
Sensory adaptation- Sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions Our sensory systems respond more strongly to changes in stimulation than to constant stimulation A stimulus that doesn’t change usually doesn’t require any action, but a change in sensory stimulus emits a need for action *

II. Vision I: How the Eyes and the Brain Convert Light Waves to Neural Signals Visual acuity- The ability to see fine detail
Snellen chart
The smallest line of letters that a typical person can read from a distance of 20 feet i. Sensing Light
Visible light is the portion of the electromagnetic spectrum that we can see Extremely small
Light waves vary in height and in the distance between their peaks, or wave-lengths Three properties of light waves
The length of a light wave determines its hue, or what humans perceive as color The intensity or amplitude of a light wave- how high the peaks are- determines what we perceive as the brightness of the light Purity is the number of distinct wavelengths that make up the light. Purity corresponds to what humans perceive as saturation, or the richness of the colors The Human Eye

Light that reaches the eyes passes first through a clear, smooth outer tissue called the cornea, which bends the light wave and sends it through the pupil, a hole in the colored part of the eye This colored part is the iris, which is a translucent, doughnut-shaped muscle that controls the size of the pupil and hence the amount of light that can enter the eye Muscles inside the...
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