Garvin Chastain

Alcohol, Neurotransmitter Systems, and Behavior

Alcohol affects several neurotransmitter systems within the brain. In this article, the author describes its effects on 5 major ones: glutamate, gamma-amino-butyric acid (GABA), dopamine, serotonin, and opioid systems. The author also notes the interactions and interdependencies of these transmitters, and provides details on both immediate effects and long-term adaptations. Last, the author explains several psychopharmacological treatments for alcoholism and the effects of these treatments on transmitters, and draws conclusions.

Feature mislocalizations and misjudgments of intercharacter distance

SummaryThree experiments were conducted to gather evidence for Wolfords (1975) feature perturbation model and claims derived from it. The first experiment found that perturbation or mislocalization of features toward the foveal center predominated when a distinctive standard for localization was presented and short-term memory factors were minimized. The second experiment found that foveal mislocalizations do seem to cause two figures in the visual field to be reported as closer to one another than they actually are presented. The final experiment provided no support for the notion that interference between figures in the visual field is caused by foveal mislocalizations making features from the figures appear to be at the same location. A distinction between mislocalizations of figures due to feature perturbations and errors due to figures which were correctly localized but not reported in the instructed order was possible in the last two experiments.

Is rapid performance improvement across short precue-target delays due to masking from peripheral precues?

The role of lateral masking in more rapid performance improvement with peripheral than with central precuing was investigated. A peripheral precue to the inside of the target location provided less masking at zero precue-target delay than a precue to the outside (experiment 1) or a precue involving a partial target at the target location (experiment 2). There was no significant interaction between precue-target delay and precue type in a comparison of inside precues and precues involving a briefly-brightened box around the target location, although overall performance was significantly poorer with the latter (experiment 3). Performance was better at short precue-target delays with inside precues than with central precues (experiment 4), yet it did not improve significantly more rapidly. Minimizing lateral masking with peripheral precues thus eliminates the dramatic performance improvement sometimes observed across short precue-target delays, causing performance to be consistently better than with central precues across these delays.

Phonological and orthographic factors in the word-superiority effect

Phonological and orthographic aspects of a letter string were found to affect the identification of a component letter in three experiments. All involved a fixed set of target vowels presented in a fixed position in letter strings. Manipulations of the phonological nature of the target or the orthographic character of the string were made by adding a letter with the postexposure mask to the original CVC trigram. In Experiment 1, the addition of an E with the mask as a final letter to the string changed the pronunciation of the target vowel, whereas the addition of an S did not. Identification accuracy was higher with the S mask. In Experiment 2, either E or D could be added to CVCs that were equally orthographic but differentially pronounceable. The same added letter had quite different effects on accuracy, depending on its effect on target pronunciation and the orthographic regularity of the string. In Experiment 3, performance on targets in orthographic CVCs was lowered to the level of nonorthographic CVCs by adding a letter that rendered the entire string nonorthographic. The results are explained by assuming that phonological and graphemic codes are developed simultaneously but maintained in a nonindependent manner.

Phonological Access to the Mental Lexicon in a Target Discrimination Task

A phonological route to the mental lexicon was demonstrated in two experiments. Each involved a target discrimination task in which the target was the first or last letter of a quadrigram. Half the quadrigrams were pseudohomophones (identical in sound but not in spelling to an English word) and the other half were nonhomophones (pronounceable but neither spelled like nor sounding like any English word). In Experiment 1 each pseudohomophone had a nonhomophone counterpart produced by changing only the letter on the opposite end of the string from the target. In Experiment 2 the nonhomophone counterparts were produced by changing only the letter next to the one on the opposite end of the string from the target; thus the extreme letters were the same for both types of quadrigrams. Performance was significantly better on pseudohomophones than on nonhomophones in both experiments.

Inhibition of Return in Visual Identification Tasks

In detection tasks, at long precue-target intervals, inhibition from precueing, rather than facilitation, has been shown. This inhibition, called “inhibition of return” (IOR), does not always occur in discrimination or identification tasks. Here in post-hoc analyses and three new experiments, evidence for IOR was shown in a target identification task using a location-cueing paradigm. In Experiments 1 and 2, a series of three cues attracted attention without eye movement, first to one of four peripheral locations, then to fixation, and then either back to the initial location or to a different one. Identification accuracy for masked visual targets was impaired when third-cue and first-cue locations matched, which constitutes evidence forIOR. In Experiment3, there was no third cue. An uninformative first cue was followed by a cue at fixation, and then a peripheral target in a “go/no-go” reaction time task. Inhibition of return was still obtained. Thus, IOR can affect identification as well as detection perf...

Confusability and interference between members of parafoveal letter pairs

In each of three experiments, confusability between members of a parafoveally exposed pair of letters affected accuracy of identifying the peripheral, but not the central, letter. Confusability was determined from a confusion matrix developed for each subject. In Experiment 1, only one letter in each pair was identified on each exposure, and the position of pair members was varied over trials while the absolute position of the pair was held at a constant distance from fixation. In Experiment 2, both letters were identified on each exposure. In Experiment 3, the criterion letter was presented at a constant distance from fixation, and both letters were identified on each exposure. Since results in Experiment 3 were the same as in Experiments 1 and 2, the effect cannot be explained with reference to an interaction between confusability and acuity. The implications of the findings for various models of visual information processing are discussed.

Identification asymmetry of parafoveal stimulus pairs

Three experiments, involving 8, 10, and 10 naive participants, respectively, were conducted to examine the phenomenon in which the peripheral member of a parafoveally appearing stimulus pair is more accurately identified than the central. In the first experiment, the asymmetry was observed with stimulus pairs which had but one distinguishing feature; this could have implications for the notion that feature perturbations between stimuli provide the basis for the effect. The second experiment eliminated an explanation based upon acuity at the position of the midpoint of the stimulus configuration, since the asymmetry remains when this position is held constant. The involvement of response or decision factors seems unlikely, since the third experiment found the effect with blocked presentations involving responses to only one member of the pair. It is concluded that accounts which appeal to difficulties in separating stimuli from the overall pair configuration fail to explain more accurate identification of the peripheral stimulus when the pair is positioned at a constant distance from fixation.

Inhibition of Return: Support for Generality of the Phenomenon

Inhibition of return (IOR), first described in 1984, was considered to be a general phenomenon for ensuring that attention would be allocated to successive stimuli in the environment. In the present research, IOR was expressed in forced-choice identification tasks with either reaction time or accuracy as the dependent measure. Thus, the generality of IOR was supported, because response inhibition cannot explain IOR found with accuracy measures. Concepts from the variable and permeable filters metaphor are used to suggest how changes in attention can change expression of IOR by rapid variation in perceptual threshold.

Timing of facilitatory and inhibitory effects of visual attention

Three experiments were conducted to investigate influences on the precue-to-target delay at which response facilitation is first replaced by inhibition of return (IOR). In Experiment 1, different ranges of delays were used; the interpolated delay at which faster RTs for matching precue and target locations changed to slower RTs was inversely related to the length of the range of precue-to-target delays within a block of trials. These findings were replicated in Experiment 2, which additionally showed that task difficulty provided an insufficient explanation for the delay in the changeover time. These data allowed the conclusion that a shorter range of precue-to-target delays results in later onset of IOR than does a longer range of delays. The data from Experiment 3 suggested that a single character on the target screen confounds the interpretation of possible facilitation and/or inhibition due to the allocation of attention. These results were related to other reported findings and to theories of attention allocation.