SUBLIMINAL PERCEPTION
SUBLIMINAL PERCEPTION
A subliminal message is a signal or message embedded in another object, designed to pass below the normal limits of perception. These messages are indiscernible by the conscious mind, but allegedly affect the subconscious or deeper mind. Subliminal techniques have occasionally been used in advertising and propaganda; the purpose, effectiveness and frequency of such techniques is debated. Subliminal perception occurs whenever stimuli presented below the threshold or limen for awareness are found to influence thoughts, feelings, or actions. The term subliminal perception was originally used to describe situations in which weak stimuli were perceived without awareness. In recent years, the term has been applied more generally to describe any situation in which unnoticed stimuli are perceived.
CONCEPT
The concept of subliminal perception is of considerable interest because it suggests that peoples' thoughts, feelings and actions are influenced by stimuli that are perceived without any awareness of perceiving. This interest was reflected in some of the earliest psychological studies conducted during the late 1800s and early 1900s. In these early studies, people were simply asked whether or not they were aware of perceiving. For example, visual stimuli such as letters, digits, or geometric figures were presented at such a distance from observers that they claimed either not to see anything at all or to see nothing more than blurred dots. Likewise, auditory stimuli such as the names of letters were whispered so faintly that observers claimed that they were unable to hear any sound whatsoever. To test whether these visual or auditory stimuli may have been perceived despite the statements to the contrary, the observers were asked to make guesses regarding the stimuli.
Example: If half the stimuli were letters and half the stimuli were digits, the observers may have been asked to guess whether a letter or a digit had been presented. The consistent result found in these early studies was that the observers' guesses regarding the stimuli were more correct than would be expected on the basis of chance guessing. In other words, despite the observers' statements indicating that they were unaware of perceiving the stimuli, their guesses indicated that they did in fact perceive sufficient information to make accurate guesses regarding the stimuli. Over the years, there have been literally hundreds of studies following a similar format. Taken together, these studies show that considerable information capable of informing decisions and guiding actions is perceived even when observers do not experience any awareness of perceiving.
Another way in which subliminal perception has been demonstrated in controlled laboratory studies is by showing that stimuli can be perceived even when they are presented under conditions that make it difficult if not impossible to distinguish one stimulus from another stimulus. The classic studies were conducted in the 1970s by the British psychologist Anthony Marcel. These experiments were based on previous findings indicating that a decision regarding a stimulus is facilitated or primed when the stimulus follows a related stimulus. For example, if an observer is asked to classify a letter string as either a word (e.g., doctor, bread) or a nonword (e.g., tocdor, dreab), a letter string such as the word doctor will be classified as a word faster when it follows a semantically related word (e.g., nurse) than when it follows a semantically non-related word (e.g., butter). Marcel found that words facilitated or primed subsequent word/nonword decisions to letter strings even when the words were presented under conditions that made it difficult if not impossible for the observers to distinguish when the words were present from when the words were absent. Since the time of Marcel's original experiments, there have been many other studies that have used similar methods. Not only have these studies confirmed Marcel's original findings, but they have shown that other stimuli such as pictures, faces, and spoken words can also facilitate subsequent decisions when they are presented under conditions that make it difficult to discriminate one stimulus from another stimulus. Although questions have been raised regarding whether the observers in these studies were completely unable to discriminate one stimulus from another stimulus, the one firm conclusion that can be made on the basis of these studies is that considerable information is perceived even when observers experience little or no awareness of perceiving as indicated by their difficulty in discriminating one stimulus from another stimulus.
Examples of subliminal perception are found in studies of patients with neurological damage. A striking characteristic of a number of neurological syndromes is that patients claim not to see particular stimuli but nevertheless respond on the basis of information conveyed by these stimuli. One example is a syndrome called blindsight. Patients with blindsight have damage to the primary visual cortex. As a result of this damage, they are often unaware of perceiving stimuli within a restricted area of their visual field. For example, if the visual field is thought of as consisting of four quadrants, a blindsight patient may have normal vision for stimuli presented in three of the quadrants but be completely unaware of stimuli presented in the fourth quadrant. However, even though these patients may claim not to see stimuli located within the "blind" quadrant, they are still able to guess the size, shape or orientation of the stimuli that they claim not to see. Another neurological syndrome in which subliminal perception occurs is prosopagnosia or face agnosia. Patients with prosopagnosia are unable to recognize familiar faces. Although they may be aware that they are looking at a person's face, they are unable to say who the person may be. Thus, prosapagnosics have no awareness of perceiving any information regarding whose face they may be viewing. However, despite this absence of awareness, some patients with prosapagnosia are able to choose which of two names goes with each familiar face that they claim not to be able to recognize.
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