User:Zyskes/sandbox

The Corollary Discharge Theory (CD) of motion perception helps understand how the mind can detect motion through the visual system, even though the body is not moving. When a signal is sent from the motor cortex of the brain to the eye muscles, a copy of that signal (see efference copy) is sent through the brain as well. The body does this in order to determine the motion of objects in reality. The two signals are then believed to be compared somewhere in the brain. This structure has not yet been identified, but it is believed to be the Medial Superior Temporal Area (MST). These two signals need to be compared in order to determine if the change in vision was caused by eye movement or movement in the world. If the two signals cancel then no motion is perceived, but if they do not cancel then the residual signal is perceived as motion in the real world. Without CD signal, the world would seem to spin around us every time we moved our eyes. It is important to note that CD and efference copy are sometimes used synonymously, they were originally coined for much different applications, with CD being used in a much broader sense.

Discovery[edit]
The first scientific research study looking at Corollary Discharge was done by Descartes in 1664 when he published his book the Treatise of Man. He was studying apparent motion and developed early theories in an error of the efferent signals centuries before Corollary Discharge theories developed. In his experiment he would take his finger and press it on the side of his eye. In doing this he would move the image across his retina. A signal was then sent to the brain saying that the image had moved and because there was no efference copy signal sent as well, his brain perceived motion. The term Corollary Discharge was finally coined in 1950 by Sperry while doing studies on fish.

Physiology[edit]
When trying to map out how CD works in the brain, it is important to begin with the Superior Colliculus (SC). It is responsible for receiving visual signals from the retina.In studies done on primate brains, a CD pathway has been found to begin in the SC. After receiving current information about the visual field, a CD signal is sent from the SC to the Frontal Eye Field (FEF), via the medial dorsal nucleus of the thalamus (MD). The FEF plays a very important role when it comes to eye movements.Particularly the FEF is responsible for much of the saccadic eye movements that eyes make. Once the FEF is activated by the CD signal, it sends a predictive signal to the occipital lobe. This signal essentially predicts what the visual field should look like after an eye movement. A signal is sent back from the occipital lobe to the FEF describing actual visual input.

In cognitive psychology, the missing letter effect refers to the finding that, when people are asked to consciously detect target letters while reading text, they miss more letters in frequent, function words (e.g. the letter "h" in "the") than in less frequent, content words. The missing letter effect has also been referred to as the reverse word superiority effect, since it describes a phenomenon where letters in more frequent words fail to be identified, instead of letter identification benefitting from increased word frequency.

The effect is usually measured using a paper-and-pencil procedure, where readers are asked to circle a target letter every time they come across it while reading a short passage. The missing letter effect is more likely to appear when reading words that are part of a normal sequence, than when words are embedded in a mixed-up sequence (e.g. readers asked to read backwards).

Early Hypotheses[edit]
Two primary hypotheses tried to explain the missing letter effect: Healy (1994) emphasized identification processes playing a crucial role, almost entirely focusing on word frequency. This hypothesis is primarily referred to as the unitization model.

However, Koriat & Greenberg (1994) viewed the structural role of the word within a sentence (i.e. function words vs. content words) to be crucial. Both accounts were thoroughly investigated, but neither could completely explain the effect.

Contemporary Hypotheses
A new model called the guidance-organization model was recently proposed to potentially explain the missing letter effect. It is a combination of the two models proposed by Healy, Koriat, and Greenberg. As Greenberg et al. explain: "The time spent processing high-frequency function words at the whole-word level is relatively short, thereby enabling the fast and early use of these words to build a tentative structural frame." Klein and Saint-Aubin proposed the attentional-disengagement model similarly includes aspects of the two earlier models but emphasizes the role of attention in reading and comprehension. They suggest that attention disengages faster from functional words than content words leading to the missing letter effect.