Perception

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Distal and Proximal

Gestalt Laws

Perceptual Constancies

Gibson’s Ecological approach Theory

Perception as a solving problem process

Attention is the cognitive process of selectively concentrating on one aspect of the environment while ignoring other things. Examples include listening carefully to what someone is saying while ignoring other conversations in the room (the cocktail party effect) or listening to a cell phone conversation while driving a car^[1]. Sometimes attention shifts to matters unrelated to the external environment, a phenomenon referred to as mind-wandering or "spontaneous thought". Attention is one of the most intensely studied topics within psychology and cognitive neuroscience.

William James, in his monumental Principles of Psychology (1890), remarked:

"Everyone knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrained state which in French is called distraction, and Zerstreutheit in German." ^[2]

Dichotic Lisening

Colin Cherry and Donald Broadbent, among others, performed experiments on dichotic listening. In a typical experiment, subjects would use a set of headphones to listen to two streams of words in different ears and selectively attend to one stream. After the task, the experimenter would question the subjects about the content of the unattended stream.

In cognitive psychology, dichotic listening is a procedure commonly used to investigate selective attention in the auditory system. In dichotic listening, two different auditory stimuli (usually speech) are presented to the participant simultaneously, one to each ear, normally using a set of headphones. Participants are asked to attend to one or (in a divided-attention experiment) both of the messages. They may later be asked about the content of either message.

In a selective attention experiment, the participant may be asked to repeat aloud the content of the attended message, a task known as shadowing. As Cherry (1953)^[1] found, people recall even the shadowed message poorly, suggesting that most of the processing necessary to shadow the attended message occurs in working memory and is not preserved in the long-term store. Performance on the unattended message is, of course, much worse. Participants are generally able to report almost nothing about the content of the unattended message. In fact, a change from English to German in the unattended channel usually goes unnoticed. However, participants are able to report that the unattended message is speech rather than non-verbal content.

Tim Rand[1] demonstrated dichotic perception in the late 1960s and early 1970s at Haskins Laboratories^[2]. This demonstration was originally known as "the Rand effect" but was subsequently renamed as "dichotic release from masking" and then "dichotic perception" or "dichotic listening." Another example of a dichotic listening experiment is Jim Cutting's (1976) demonstration^[3] at Haskins Laboratories that listeners could correctly identify syllables when different components of the syllable were presented to different ears. The formants of vowel sounds and their relation are crucial in differentiating vowel sounds. Yet even though listeners heard two separate signals (no ear received a 'complete' vowel sound), they could identify the syllable sounds.

Dichotic listening can also be used to test the hemispheric asymmetry of a cognitive function such as language processing. In the late 1960s and early 1970s Donald Shankweiler [2] and Michael Studdert-Kennedy [3] of Haskins Laboratories used a dichotic listening technique (presenting different nonsense syllables simultaneously to opposite ears) to demonstrate the dissociation of phonetic (speech) and auditory (nonspeech) perception by finding that phonetic structure devoid of meaning is an integral part of language, typically processed in the left cerebral hemisphere^[4][5][6]. A dichotic listening performance advantage for one ear is interpreted as indicating a processing advantage in the contralateral hemisphere. In another example, Sidtis (1981)^[7] found that healthy adults have a left-ear advantage on a dichotic pitch recognition experiment. He interpreted this result as indicating right-hemisphere dominance for pitch discrimination.

Feature Integration Theory

Anne Treisman developed the highly influential feature integration theory^[3]. According to this model, attention binds different features of an object (e.g., color and shape) into consciously experienced wholes. Although this model has received much criticism, it is still widely accepted or held up with modifications as in Jeremy Wolfe's Guided Search Theory.

The feature integration theory, developed by Treisman and Gelade since the early 1980s has been one of the most influential psychological models of human visual attention. According to Treisman, in a first step to visual processing, several primary visual features are processed and represented with separate feature maps that are later integrated in a saliency map that can be accessed in order to direct attention to the most conspicuous areas.

Treisman distinguishes two kinds of visual search tasks, feature search and conjunction search. Feature search can be performed fast and pre-attentively for targets defined by primitive features. Conjunction search is the serial search for targets defined by a conjunction of primitive features. It is much slower and requires conscious attention. She concluded from many experiments that color, orientation, and intensity are primitive features, for which feature search can be performed.

It was widely speculated that the saliency map could be located in early visual cortical areas, e.g. the Primary Visual Cortex (V1), though this is controversial. Wolfe's popular Guided Search Model has many similarities to the feature integration theory.

Visual search

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The more distractors there are, the longer it takes to find the letter B in the array

Feature search: The red X is a color singleton, the O is a shape singleton. Both can be found efficiently.

Conjunction Search: Find the orange square

Visual search is a type of perceptual task requiring attention. Visual search involves an active scan of the visual environment for a particular object or feature (the target) among other objects or features (the distracters). Visual search can take place either with or without eye movements. Common examples include trying to locate a certain brand of cereal at the grocery store or a friend in a crowd (e.g. Where's Waldo?). The scientific study of visual search typically makes use of simple, well-defined search items such as oriented bars or colored letters.

The efficiency of visual search depends on the number and type of distracters that may be present. Search tends to be more efficient when the target is very different from the distracters. The number of targets and distractors in a given visual array is called the display size. The display size effect is the degree to which task performance (Reaction time and/or accuracy) depends on the display size. The magnitude of the display size effect can vary greatly, from effectively zero (e.g., in searches for a red target among green distracters, called a feature search) to a large effect (e.g., in searches for a red X among green Xs and red Os, called a conjunction search). Search tasks with a small display size effect are referred to as "efficient;" search tasks showing a large display size effect are termed "inefficient."

Types of search

Feature Search

Feature Search is the process of searching for targets defined by a unique visual feature, such as color, size, orientation or shape. Feature searches are typically efficient. For instance, an O is rapidly found among Xs, and a red target is rapidly found if all the distracters are black (see illustrations).

Conjunction Search

Conjunction Search occurs when a target stimulus is defined not by any single visual feature, but by a combination of two or more features. An example is search for an orange square among blue squares and orange triangles (see illustration): neither the single feature "orange" nor the feature "square" is sufficient in isolation to uniquely specify the search target.

Conjunction searches are typically inefficient, with the time to complete the search task increasing linearly with the number of distractors. This behavior is as if the subject were forced to examine each item in the search array one at a time before deciding whether or not it was the search target, leading to the term "serial search".

Theories of Visual Search

Biological Correlates

In the 1960s, Robert Wurtz at the National Institutes of Health began recording electrical signals from the brains of macaques who were trained to perform attentional tasks. These experiments showed for the first time that there was a direct neural correlate of a mental process (namely, enhanced firing in the superior colliculus).

In the 1990s, psychologists began using PET and later fMRI to image the brain in attentive tasks. Because of the highly expensive equipment that was generally only available in hospitals, psychologists sought for cooperation with neurologists. Pioneers of brain imaging studies of selective attention are psychologist Michael I. Posner (then already renown for his seminal work on visual selective attention) and neurologist Marcus Raichle. Their results soon sparkled interest from the entire neuroscience community in these psychological studies, which had until then focused on monkey brains. With the development of these technological innovations neuroscientists became interested in this type of research that combines sophisticated experimental paradigms from cognitive psychology with these new brain imaging techniques. Although the older technique of EEG had long been to study the brain activity underlying selective attention by cognitive psychophysiologists, the ability of the newer techniques to actually measure precisely localized activity inside the brain generated renewed interest by a wider community of researchers. The results of these experiments have shown a broad agreement with the psychological, psychophysiological and monkey literature.

Current research

Attention remains a major area of investigation within psychology and neuroscience. Many of the major debates of James' time remain unresolved. For example, although most scientists accept that attention can be split, strong proof has remained elusive. And there is still no widely accepted definition of attention more concrete than that given in the James quote above. This lack of progress has led many observers to speculate that attention refers to many separate processes without a common mechanism.

Areas of active investigation involve determining the source of the signals that generate attention, the effects of these signals on the tuning properties of sensory neurons, and the relationship between attention and other cognitive processes like working memory.

[edit] Clinical model of attention

Many times, clinical models differ from investigation models. This is the case of attention models. One of the most used models for the evaluation of attention in patients with very different neurologic pathologies is the model of Sohlberg and Mateer.^[4] This hierarchic model is based in the recovering of attention processes of brain damage patients after coma. Five different kinds of activities of growing difficulty are described in the model; connecting with the activities that patients could do as their recovering process advanced.

Focused attention: This is the ability to respond discretely to specific visual, auditory or tactile stimuli.

Sustained attention: This refers to the ability to maintain a consistent behavioral response during continuous and repetitive activity.

Selective attention: : This level of attention refers to the capacity to maintain a behavioral or cognitive set in the face of distracting or competing stimuli. Therefore it incorporates the notion of "freedom from distractibility"

Alternating attention: it refers to the capacity for mental flexibility that allows individuals to shift their focus of attention and move between tasks having different cognitive requirements.

Divided attention: This is the highest level of attention and it refers to the ability to respond simultaneously to multiple tasks or multiple task demands.

This model has been shown to be very useful in evaluating attention in very different pathologies, correlates strongly with daily difficulties and is especially helpful in designing stimulation programmes such as APT (attention process training), a rehabilitation programme for neurologic patients of the same authors.

[edit] Overt and covert attention

Attention may be differentiated according to its status as 'overt' versus 'covert'. Overt attention is the act of directing sense organs towards a stimulus source. Covert attention is the act of mentally focusing on one of several possible sensory stimuli. Covert attention is thought to be a neural process that enhances the signal from a particular part of the sensory panorama.

There are studies that suggest the mechanisms of overt and covert attention may not be as separate as previously believed. Though humans and primates can look in one direction but attend in another, there may be an underlying neural circuitry that links shifts in covert attention to plans to shift gaze. For example, if individuals attend to the right hand corner field of view, movement of the eyes in that direction may have to be actively suppressed.

The current view is that visual covert attention is a mechanism for quickly scanning the field of view for interesting locations. This shift in covert attention is linked to eye movement circuitry that sets up a slower saccade to that location.

[edit] Neural correlates of attention

Most experiments show that one neural correlate of attention is enhanced firing. If a neuron has a certain response to a stimulus when the animal is not attending to the stimulus, then when the animal does attend to the stimulus, the neuron's response will be enhanced even if the physical characteristic of the stimulus remains the same. A strict criterion in this paradigm of testing attention is that the physical stimulus available to the subject must be the same, and only the mental state is allowed to change. In this manner, any differences in neuronal firing may be attributed to a mental state (attention) rather than differences in the stimulus itself.

Wiki

Perception

Jeremy Wolfe Publications

How the Deployment of Attention Determines what we see. Anne Treisman

Anne Treisman- object tokens