Parafoveal Stimuli Research Articles

Semantic processing of unattended parafoveal words

The influence that a context word presented either foveally or parafoveally, may exert on the processing of a subsequent target word was studied in a semantic decision task. Fourteen subjects participated in the experiment. They were presented with word-nonword pairs (prime). One member of the pair (which the subjects had to attend to) appeared centrally, the other parafoveally. The prime was followed by a target at two inter-stimulus intervals (ISI; 200 and 2000 msec). The word stimulus of the pair could be semantically related or unrelated to the target. The subjects' task was to classify the target as animal or not animal by pressing one of two buttons as quickly as possible. When the target word was semantically associated with the foveal (attended) word the reaction times were faster for both ISIs; when it was associated with the parafoveal (unattended) word in the prime pair, there were facilitatory effects only in the short ISI condition. A second experiment was run in order to evaluate the possibility that the obtained results were due to identification of the parafoveal stimulus. The same prime—target pairs of experiment 1 (without the target stimuli) were used. The prime—target pairs were presented to fourteen subjects who were requested to name the foveal (attended) stimulus and subsequently, if possible, the parafoveal (unattended) one. Even in this condition, percentage of identification of the unattended word was only 15%, suggesting that previous findings were not due to identification of unattended stimuli. Results are discussed in relation to Posner and Snyder's (1975) dual coding theory.

On the nature of perceptual limits in vision. A new look at lateral masking.

Studies of attention have generally assumed that the principal limit to visual perception involves the capacity to identify a stimulus. Analyses of responses in visual tasks, however, suggest that errors can arise from a loss of position information, as well as a loss of identity information, and that these two types of errors may be affected by different variables. Based on this, we have proposed that the difficult aspect of perception is not that of recognizing the form of the stimulus but rather determining its position relative to other items in the field. To demonstrate this, we conducted a series of experiments on lateral masking that showed that the failure to perceive a parafoveal stimulus surrounded by other items is due to two quite separate components: a loss of identity information induced by the immediately adjacent items and a loss of position information induced by both adjacent and non-adjacent items.

Automatic and Controlled Semantic Priming: Accuracy, Response Bias, and Aging

Adult age differences in automatic and controlled semantic priming were investigated by varying the probability of valid primes in a lexical decision task. Tachistoscopic parafoveal stimulus presentation was used to assess age differences in accuracy and response bias as well as latency. Both age groups showed the expected findings of benefits without costs under automatic priming and benefits and costs under controlled priming. Errors for young adults were distributed equally among word and nonword stimuli, whereas older adults displayed a strong tendency to commit errors on nonword trials.

Parafoveal attention in congenitally deaf and hearing young adults

This reaction-time study compared the performance of 20 congenitally and profoundly deaf, and 20 hearing college students on a parafoveal stimulus detection task in which centrally presented prior cues varied in their informativeness about stimulus location. In one condition, subjects detected a parafoveally presented circle with no other information being present in the visual field. In another condition, spatially complex and task-irrelevant foveal information was present which the subjects were instructed to ignore. The results showed that although both deaf and hearing people utilized cues to direct attention to specific locations and had difficulty in ignoring foveal information, deaf people were more proficient in redirecting attention from one spatial location to another in the presence of irrelevant foveal information. These results suggest that differences exist in the development of attentional mechanisms in deaf and hearing people. Both groups showed an overall right visual-field advantage in stimulus detection which was attenuated when the irrelevant foveal information was present. These results suggest a left-hemisphere superiority for detection of parafoveally presented stimuli independent of cue informativeness for both groups.

Parafoveal visual information and semantic contextual constraints.

Two experiments are reported that examine the influence of semantic contextual constraints on an individual's ability to use parafoveal visual information. Subjects were presented either a word (reptile) or a row of Xs in foveal vision along with a parafoveal nonword (snckks) centered 2.3 degrees or 5 degrees to the left or right of fixation. The subjects were asked to pronounce the parafoveal stimulus aloud. During their eye movement to that stimulus, the nonword was replaced by a word that was either (a) semantically related to the foveal item and visually related to the parafoveal preview nonword (snakes), (b) semantically unrelated to the foveal item and visually related to the preview (sneaks), (c) semantically related to the foveal item and visually unrelated to the preview (lizard), or (d) semantically unrelated to the foveal item and visually unrelated to the preview (limits). In Experiment 1, subjects were only given 250 msec to use the semantic context, whereas in Experiment 2, subjects were given 1,250 msec. The results of both experiments yielded highly significant effects of contextual constraints and parafoveal visual information. However, the first experiment yielded additive effects of the two variables, whereas the second experiment yielded interactive effects. The results are discussed in light of recent arguments regarding the importance of contextual constraints for the use of parafoveal visual information.

Parafoveal word perception: A further case against semantic preprocessing.

Three experiments were performed to explore the processing of parafoveal information. A foveal and a parafoveal word pair were presented within the time frame of a single fixation, but short enough to prevent successful refixation of the parafoveal word. Subjects reporting partial parafoveal word information were not able to use this information to bias their choice in a forced-choice task requiring some semantic information from the parafoveal word for correct performance. This result was observed even though correct parafoveal word identification was facilitated if the foveal stimulus was related to the parafoveal word. Further, the data strongly suggest that information is obtained initially from the fixated words, regardless of whether foveal word presentation precedes or follows the parafoveal stimulus.

Asymmetric identification of parafoveal stimulus pairs: feature perturbations on failure in feature extraction?

Asymmetric identification of parafoveal stimulus pairs: feature perturbations on failure in feature extraction?

A distractive effect of peripheral attention on foveal trigram recognition.

The recognizability of tachistoscopically presented foveal trigrams was investigated as a function of paying attention, or not paying attention, to simultaneously exposed parafoveal trigrams. The same set of stimuli was presented in both conditions. All six observers made a significant number of errors at 50 ms stimulus duration in the attentive condition. This occurred even though they could not correctly report the parafoveal stimulus. Performance reached 95% correct at 200 ms stimulus duration, just when parafoveal trigrams were occasionally identified. At 50 ms stimulus duration in the attentive condition, errors were more marked for non-wordlike center trigrams. When the parafoveal trigram was non-wordlike, its distractive effect was greater than when it was wordlike. Neither distance nor position of the parafoveal trigrams were significant factors. The distractive effect of peripheral attention on recognition of letter stimuli suggests that information from parafoveal stimuli is available through attention. The results do not suggest that during a short exposure parafoveal information triggers attention: they rather indicate that conscious attention determines the processing of parafoveal stimuli.

Effect of selective adaptation on detection of simple and compound parafoveal stimuli

Detection thresholds for peripherally viewed circular stimuli with diameters ranging from 0.5 to 4° were measured before and after adaptation with 1.5, 2.5 and 3.5° circular stimuli. Thresholds were also measured for compound stimuli, formed by superimposing 1, 2, 3 and 4° stimuli upon a 4° stimulus, both before and after selective adaptation. The results indicate that an adaptation stimulus is most effective in reducing the visibility of stimuli nearest in size to the adaptation stimulus, but when the adaptation stimulus differs in size from the test stimulus, the effect is reduced and in some cases reversed. The results are discussed in terms of their implications for certain models of spatial integration in vision.

Relative Effectivity of Foveal and Parafoveal Stimuli in Eliciting Fusion Movements of Small Amplitude

The relative effectivity of foveal and parafoveal stimuli in eliciting fusion movements has been evaluated by measuring the maximum amount of adduction which can be elicited by such stimuli. It was concluded that the amplitude of adduction declined precipitously as the stimuli were presented to more and more eccentric retinal regions.¹ Figure 1 illustrates the type of targets used to elicit adduction of the left eye. When duction at the fovea is being tested, the right eye fixates the white dot in the center of the rectangle shown in the upper right half of Fig 1. When duction elicited by extrafoveal stimuli is being measured, the right eye fixates the white dot shown in the lower half of Fig 1. The centers of the rectangles presented to both the right and the left eyes are located at either 0, 0.25, 2, or 4 degrees to the right of the

RELATIVE EFFECTIVITY OF FOVEAL AND PARAFOVEAL STIMULI IN ELICITING FUSION MOVEMENTS.

<h3>Introduction</h3> Present opinion seems to be that stimuli presented to the peripheral retinas are more powerful in eliciting fusion movements than are stimuli presented to the foveas. In an annual review of the literature on strabismus, Parks,¹when discussing an investigation by Nauheim,²says, "Peripheral fusion is stronger than central fusion. That this is so was not questioned...." Parks then proceeds to discuss an hypothesis to account for the superiority of the peripheral retina. Linksz³in an annual review of optics and visual physiology quotes Nauheim's * statement that "paramacula targets represent a greater stimulus to fusion than do central targets...." Linksz comments, "(Only in case the author meant 'greater stimulus for fusion<i>movements</i>,' would one, somewhat reluctantly, agree.)" This belief in the dominance of the peripheral retina has, as its natural consequence, a strong influence on thought concerning strabismus and orthoptic training. Burian⁴says, "I believe

Some Characteristics of Parafoveal Stimuli and their After-Images

Resume Certains effets dans le comportement des images consecutives observees dans des conditions favorables ne suivent pas la route qu'on pourrait predire a priori sur la supposition que l'image consecutive est une excitation retinienne locale ou etat qui persiste. On montre que les images consecutives qui resultent de la stimulation foveale sont influencees dans leur intensite, leur couleur, et leur duree, et surtout dans la modification progressive de forme laquelle elles subissent, par la presence d'autres images consecutives qui resultent de stimuli parafoveals presentes simultanement. On montre que celles-la souffrent, comme resultat de la presence de celles-ci, une decroissance d'intensite et de duree laquelle depasse la decroissance soufferte quand elles sont presentees seules. Il peut y avoir une obliteration complete de l'image consecutive negative du stimulus foveal. L'aire du stimulus parafoveal se montre le facteur efficace dans la production de cet effet affaiblissant. Quelques-uns des effet...