User:Psy463 9971/Subliminal Semantic Activation

Definitions for Subliminal Semantic Activation
Subliminal Semantic Activation (SSA) is, “defined as evidence for analysis of a word’s meaning under conditions that prevent awareness of the word’s physical presence”. Another commonly accepted operation definition of SSA is, “a pattern of data showing statistically significant indirect effects for stimuli that produce no evidence of direct effects”. It is an occurence in which consciously unperceptible stimuli (subliminal stimuli) are still able to be mentally processed, and therefore have an effect on future perceptions.

Conscious Awareness: Liminal vs. Subliminal Stimuli
Before discussing how scientists have studied SSA, it is imperative to understand the difference between liminal (consciously perceivable) and subliminal (consciously unperceivable) stimuli. First, however, conscious awareness must be defined. Conscious awareness of an event is the realization that the said event occurred. That is, we can think about it and we know what it is that we are thinking of. In a television commercial, when a brand name appears on the screen, we notice it, we have the ability to think about it, and thus we are consciously aware of it. If a person is not consciously aware of what they perceive, the stimulus is said to be subliminal -- we cannot "think" about it. For example, if a word is flashed on a screen at a rate that is too quick for a person to realize that it appeared, it (i.e., the word) has not been consciously perceived; but, the word still may have been subliminally perceived. This subliminal perception is the focus of scientists who have studied SSA.

Subjective Threshold vs. Objective Threshold
It is the "line of awareness", this threshold, that distinguishes limenal and subliminal stimuli. The objective threshold is the, "highest level of stimulus presentatoin (i.e., duration, energy, or signal-to-noise ration) at which force-choice responding indicates that the stimulus is undetectable". The subjective threshold is the, "highest level of stimulus presentation at wihch subjects report [...] a lack of awareness. The subjective threshold, which should be associated with greater stimulus energy than the objective threshold, is expected to be associated also with above-chance performance on direct measures". In these views, SSA is, "defined as [an] occurence of indirect effects of stimuli that fall in the range between objective and subjective thresholds". Therefore, scientists have sought to study how stimuli that fall below the objective threshold and above the subjective threshold, thus being subliminal (below conscious awareness), affect future perceptions. These subliminal stimuli, used in a method called priming (discussed later), are the primary means for exploring SSA.

Direct and Indirect Effects
Direct effects are the effects of a stimulus on the subjects' instructed responses to that stimulus, and are usually assessed on the accuracy of the response to the task. Indirect effects are the uninstructed effects of a stimulus that has been masked (discussed later) on the subjects' behavior.

Beginnings of Subliminal Semantic Activation Research
A.J. Marcel reported findings of the indirect-without-direct-effect data patterns, indicating SSA, in 1980 and 1983. Other investigators produced similar effects, but Daniel Holender soon after called Marcel’s findings into question. In his 1986 article about semantic activation, Holender found Marcel’s procedures did not, “ensure that semantic activation was not accompanied by conscious identification of the stimulus at the time of presentation”. Holender found that Marcel had limitations in the sensitivity of his direct measures.

Cheesman and Merikle supported Holender’s findings by being unable to reproduce Marcel’s indirect-without-direct effect data pattern when using direct measures that were more sensitive than Marcel. Cheesman and Merikle, however, did offer an alternative interpretation that provided more easily obtainable support for SSA. In their 1984 and 1986 articles, they found that indirect effects may be obtained when the perception of the subliminal stimulus was below the subjective threshold, yet while not in the absence of direct effects (i.e., not an objective threshold on the direct measure). They found that only stimuli above the subjective threshold were consciously perceived. Thus, any direct effects witnessed for subliminal stimuli must therefore be unprocessed by unconscious cognition.

Reingold and Merikle subsequently came out with the inclusiveness assumption, which stated that performance on direct and indirect measures can be reflective of both conscious and unconscious cognition. They demonstrated their inclusiveness assumption to provide evidence for unconscious cognition.

Methodology for Testing SSA
" Subliminal semantic activation is most often investigated with priming procedures".

Priming
Researchers often use priming procedures to test for SSA. Primes are presented before target stimuli. They are meant to elicit attitudes and behaviors that are relative to the nature of the prime.

Visual masking & making stimuli subliminal
In visual masking, the prime's visibility is reduced or eliminated by a second, brief stimulus. The second, brief stimulus is the mask. The mask can be any sort of stimulus that disrupts the subjects ability to perceive the prime. The mask can occur prior, simultaneous to, and/or following the prime. Furthermore, if the subject claims not to be able to discern any sort of meaning from the target or prime, they are said to be subliminal.

Stimulus Onset Asynchrony
The interval of time between the prime and the target is called the prime-target stimulus onset asynchrony (SOA). In Greenwald et al.'s (1996) experiments, the interval between the appearances of primes and targets ranged from 67 to 400 miliseconds.

Two-choice categorization task
A fundamental method of testing for SSA has subjects performing a two-choice categorization task. The task is, “supplemented by the presentation of a subliminal prime word shortly before each to-be-judged target stimulus word”. The two categorization tasks used to test for the effects subliminal priming have subject decide if a target letter string forms a word, or if a target word is pleasant or unpleasant. These tasks can be performed on a computer, in which subjects use their right and left hands to press a button that corresponds to their response to the target. Furthermore, researchers make use of response windows (allowed time per response) in experiments involving computer displays, a procedure which, when combined with visual masking (masked priming), “reliably produces statistically strong subliminal priming effects”.

In Greenwald et al.'s (1996) study on SSA, subjects were primed with affectively polarized words (categorized as pleasant and unpleasant in meaning), or common names (categorized as male or female). The targets used were polarized words that were either congruent or incongruent to the prime. An example of prime-targetcongruent words would is"lucky"-"diamond", and an example of incongruent prime-target words is "lucky"-"cancer". The SOAs varied between 67 to 400 ms. For example, a prime with the word "lucky" would be masked and followed by a either a subliminal congruent or incongruent (in evaluative pleasantness) target word. The subjects were then to determine if the target word was pleasant or unpleasant, within a given amount of time. The subjects were measured based on the accuracy of their determination of the evaluation of the target word with respect to the prime, and the amount of time they took to respond following the target. It is said that priming occurs when, "the meaning of the prime affects the speed or accuracy of response to the target".

Linear Regression Analysis
Greenwald et al. (1995) found that using a linear regression analysis analysis method to analyze data obtained in the experiments allowed statistically significant evidence for SSA to be reached.

People perceive subliminal stimuli
Greenwald, Drains, & Abrams (1996), have found that, “the central nervous system monitors stimuli outside its current focus of attention.” Furthermore, Greenwald et al., found that activation is very short-lived, with the target word needing to occur within 100 milliseconds of the subliminal prime, but that indeed, visually masked prime words have the ability to influence the meanings of future words. These findings enabled them to conclude that, “the occurrence of semantic activation by consciously unperceived primes indicates that semantic activation does not depend on the prime reaching working memory (awareness)”.

Mental mapping of subliminal primes
The nature of the two-choice categorization tasks had some researchers concerned that priming is driven by automation of motor responses. That is, word associations made in practice elicit responses that, when the word is later presented as a subliminal prime, activate a word-response mapping that directs the subject to pick the side that correctly corresponds to the prime. Abrams, Klinger, & Greenwald (2002), however, found that in fact, “associations formed in practice that underlie subliminal priming are between words and semantic categories.” Priming is driven by “word-to-category” mapping, and that, “subliminal priming involves unconscious categorization of the prime.” Therefore, practiced subliminal words activate semantic categories, rather than activating automatic word-response mappings, further supporting unconscious cognition.

Dissociation of network paths
In 1995, Greenwald, Klinger, & Schuh, performed experiments that analyzed, “regressions of measures of indirect effects of direct effects of marginally perceptible stimuli”. The results produced evidence that supported dissociation of (multiple) network paths. That is, “direct and indirect effects of marginally perceptible stimuli might use separate network paths and, therefore, be independent of (i.e. dissociated from) one another”.