Sensation and Perception

1. Sensation and Perception By: Isaac Parsley & Austin Brewer

2. Gustav Fechner • German philosopher and experimental psychologist. An early pioneer in experimental psychology and founder of psychophysics, he inspired many 20th century scientists and philosophers. He is also credited with demonstrating the non-linear relationship between psychological sensation and the physical intensity of a stimulus via the formula: "S = K Log I", which became known as the Weber–Fechner law.

3. Absolute Threshold • Gustav Fechner (1801-1887) considered two thresholds in his analysis of sensation. The first, the absolute threshold, is the lowest intensity at which a stimulus can be detected. Like Gotfried Leibniz (1646-1716) and Johann Herbert (1776-1841) before him, he allowed for negative sensations -- unconscious reactions to stimulus intensities below absolute threshold -- and the possibility that sub-threshold stimuli can cumulate beyond absolute threshold to create a conscious sensation. For Fechner, though, the absolute threshold was of limited usefulness. It was only the lowest level of conscious sensation. His goal was to relate a full range of stimulus intensities to their resultant sensation values. In this regard, he introduced the concept of a differential threshold: the minimal amount of change in a stimulus that can be detected. He assumed the differential threshold for any stimulus within the full range of intensities to be subjectively equal, the equivalent of one jnd.

4. David Hubel with Torsten Wiesel • David H. Hubel spent many years collaborating with Torsten N. Wiesel, investigating brain function, most notably the nerve impulses that flow between retina and brain. They proved that specific nerve cells are responsible for specific types of visual comprehension, and were jointly awarded the Nobel Prize for Medicine in 1981, along with Roger W. Sperry. Hubel spent parts of his childhood on both sides of the border between Detroit and Windsor, and holds dual U.S. and Canadian citizenship.

5. Ernst Weber • A German physician who is considered one of the founders of experimental psychology. • He found that weight discrimination was much finer with active lifting than when the weights were placed on supported hands. He also found that the just-noticeable difference (jnd) of the change in the magnitude of a stimulus (viz., small weights held in the hand) is proportional to the magnitude of the stimulus (e.g., 5%), rather than being an absolute value (e.g., 5 grams). Gustav Fechner named this Weber's Law.Fechner explored this relation further in the 1850s and, integrating over Weber's proportional jnds, argued for a logarithmic relation between physical and psychological (or perceived) magnitudes. This new law became known as Fechner's Law, or the Weber-Fechner Law, and formed the basis of Fechner's new science of psychophysics.

6. Torsten Wiesel with David Hubel • Received the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was shared with Roger W. Sperry for his independent research on the cerebral hemispheres.

7. Feature detectors • Feature detection is a process by which the nervous system sorts or filters complex natural stimuli in order to extract behaviorally relevant cues that have a high probability of being associated with important objects or organisms in their environment, as opposed to irrelevant background or noise. • Feature detectors are individual neurons – or groups of neurons – in the brain which code for perceptually significant stimuli. Early in the sensory pathway feature detectors tend to have simple properties; later they become more and more complex as the features to which they respond become more and more specific. • For example, simple cells in the visual cortex of the domestic cat (Feliscatus), respond to edges – a feature which is more likely to occur in objects and organisms in the environment.[1] By contrast, the background of a natural visual environment tends to be noisy – emphasizing high spatial frequencies but lacking in extended edges. Responding selectively to an extended edge – either a bright line on a dark background, or the reverse – highlights objects that are near or very large. Edge detectors are useful to a cat, because edges do not occur often in the background “noise” of the visual environment, which is of little consequence to the animal.