Temporal preparation facilitates perceptual identification of letters

Recent evidence has suggested that perceptual processing of single stimulus features improves when participants are temporally prepared for the occurrence of the stimuli. This study was conducted to investigate whether the benefit of temporal preparation generalizes to perceptual identification of more complex stimuli, such as letters. In three experiments, participants discriminated masked letters under high- and low-temporal-preparation conditions. Visual discrimination performance in all experiments improved when the participants were temporally prepared. Therefore, the present results support the notion that perception benefits from temporal preparation not only at the feature level, but also at subsequent levels at which feature information is integrated.     

Effects of perceptual quality and visual field of probe stimulus presentation on memory search for letters

Observers indicated whether a single probe letter presented to the left visual field/right hemisphere (LVF-RH) or to the right visual field/left hemisphere (RVF-LH) was contained in a memory set of 2, 3, 4, or 5 letters. For positive trials, the increase in reaction time caused by perceptually degrading the probe letter became progressively larger as memory set size became larger when the probe was presented to the LVF-RH but not when the probe was presented to the RVF-LH. These results were obtained regardless of whether the case of the probe letter varied randomly (Experiment 1) or only capital letters were used (Experiment 2). The results on LVF-RH trials suggest a relatively visuospatial memory comparison process, whereas the results on RVF-LH trials suggest a more abstract memory comparison process. In addition to these effects, the intercept of the memory set size function was lower on LVF-RH trials than on RVF-LH trials when the probe letter was perceptually degraded, consistent with the hypothesis that the right hemisphere is more efficient than the left at early visuospatial processes. Perhaps it is this efficiency at early visuospatial processes that produces the bias toward visuospatial memory comparison on LVF-RH trials.     

Independence versus interference in the perceptual processing of letters

Several experiments are reported that help resolve the discrepancy between studies indicating that letters are perceived independently and studies showing perceptual interference between letters. Two variables were examined which, based on the existing literature, appeared to be important in distinguishing between the perceptual independence and perceptual interference studies. In Experiment 1, the amount of spatial separation between letters was varied. Surprisingly, the letters were perceived independently, regardless of the amount of separation or degree of similarity between them. Thus, it was concluded that the amount of interletter separation is not sufficient to account for the difference between studies demonstrating independence and those demonstrating interference. The results of Experiments 2 and 3 indicated that the type of perceptual limitation that is used to control response accuracy determines whether perceptual independence or interference is obtained. Specifically, perceptual interference was obtained only under masking conditions, whereas perceptual independence was obtained only under energy-limited (no-mask) conditions. Experiment 4 extended these results, indicating that perceptual interference is obtained under prestimulus as well as poststimulus masking conditions. Several interpretations of the perceptual interference data are considered, and it is concluded that the data can best be accounted for in terms of a model based on the principle of feature-specific inhibition.     

Cambridge University versus Hebrew University: The impact of letter transposition on reading English and Hebrew

Is reading similarly affected by letter transposition in all alphabetic orthographies? “The Cambridge University effect,” demonstrating that jumbled letters have little effect on reading, was examined using rapid serial visual presentation (RSVP) in English and in Hebrew. Hebrew-English bilinguals were presented sentences in both languages containing words with transposed letters. Sentences were presented rapidly on the screen word by word, and participants had to reproduce the sequence of words perceived. We found a marked difference in the effect of transpositions in the two languages. In English, transpositions had little effect on performance, whereas in Hebrew, performance deteriorated dramatically for words with transposed letters. The differential effects of transposition are accounted for by the difference in lexical organization in Hebrew and in English, suggesting that models of reading in alphabetic orthographies may be language specific.     

The perceptual fate of letters in two kinds of apparent movement displays

Two experiments investigated the importance of figurai relationships among stimulus elements in the determination of the kind of motion perceived in bistable apparentovement displays. Stimulus frames containing the words MITE and ITEM were constructed in such a way that the letters I, T, and E appeared in corresponding locations while the M was in disparate locations between frames. When the frames were alternated with a 20-msec ISI, observers maintained local figurai identity in their percepts of apparent movement. However, when the frames were alternated with an 80-msec ISI, observers reported apparent movement of the entire groups of letters and thereby ignored figurai relationships in their percepts of apparent movement. In a second experiment, it was found that figurai nonidentity between elements of successive frames always resulted in apparent movement of a perceptual group or “blob” regardless of ISI. It is suggested that short-range apparent-movement percepts rely strongly upon figurai identity among corresponding stimulus elements, whereas long-range apparent-movement percepts do not.     

Lateralization effects in the perception of Hebrew and English words

A series of four experiments was conducted on Israelis with a good knowledge of English, Anglo-Saxons with a good knowledge of Hebrew, and full Bilinguals of the two languages. In all experiments words were presented vertically and measurements of both accuracy and response times were taken. Experiments 1 and 2 examined the perception of Hebrew words in unilateral and bilateral conditions, respectively; Experiments 3 and 4 examined the perception of both Hebrew and English words in these two conditions. The results revealed right visual field advantage in the perception of words in both languages and in all groups. A reversal between the two conditions was not found. The data support the hypothesis whereby nonnative languages are less lateralized than native ones, but they indicate that full bilinguals are more, not less, lateralized than monolinguals. Various hypothesis regarding the relationship between lateralization and bilingualism are discussed.     

Children's use of perceptual set

The effects of perceptual set and of “sequential visual noise” on the identification of briefly exposed pictures were examined in 5-year-olds, 8-year-olds, and adults. Subjects were asked to indicate whether a brief target matched a standard. The standard picture was presented either before the target picture (to establish a set) or after the target. The target was presented either alone or last in a series of six brief pictures (i.e., in noise). Adults and 8-year-olds were at ceiling when the target was presented alone, but set facilitated their identification of the target in noise. The 5-year-olds benefited from set both when the target was presented alone and when it was presented in noise. These findings suggest that set for a specific target picture functions similarly at all ages.     

Absence of perceptual processing during reconfiguration of task set

The authors manipulated stimulus contrast and response-stimulus interval in the alternating runs paradigm to investigate whether early processing could be carried out during a task switch. Subjects alternated between judging the magnitude and the parity of a digit. The results suggested that early processing was not carried out during the task switch (Experiment 1), even in the absence of potentially confounding auditory or visual warning signals (Experiment 2). This processing was, however, carried out in parallel with a demanding operation in a 2nd task (Experiment 3), using the display parameters of Experiments 1 and 2 in the psychological refractory period paradigm. It is concluded that, functionally, task switching may impose a hard bottleneck even for very early stimulus processing. ((c) 2003 APA, all rights reserved)     

Effects of aging on perceptual closure

Two research strategies were employed to investigate reasons for the poorer performance associated with increased age on perceptual closure tasks involving the integration and identification of incomplete pictures. One strategy consisted of examining age differences in measures designed to reflect the proficiency of processing components presumed to be involved in the closure task. The performance of older adults was significantly worse than that of young adults on each measure, suggesting that the age differences in the criterion task could not be localized in a single specific component. The second strategy involved determining whether young and old adults differed in the effects of practice or in the amount of specific and general transfer resulting from that practice. No age differences other than those in the overall level of performance were discovered, indicating that the age-associated problem may be independent of the processes contributing to the acquisition and transfer of new information. It was suggested that the age differences in perceptual closure tasks originate because of a general inefficiency in information processing due to a reduction in some type of general-purpose processing resource, and not because of a limitation in a single specific process.     

Directional tendencies of Hebrew, Japanese, and English readers.

Consistent left-right and right-left reading habits are associated with corresponding directional tendencies in the reproduction of horizontally displayed visual stimuli. Inconsistent reading habits should therefore be associated with inconsis tent directional tendencies. This hypothesis was tested on Japanese readers whose reading habits were inconsistent by asking them to reproduce four series of 12-item horizontal stimulus arrays. The hypothesis was partially supported by the data which showed that, like Hebrew readers who also have inconsistent reading habits, the directional tendencies shown by the 68 Japanese readers were significantly weaker on some tasks that those shown by the 16 English readers whose left-right reading habits were consistent. The data were interpreted as showing that acquired reading habits may affect directionality in perception of visual stimuli.     

The effects of perceptual set on the shape and apparent depth of subjective contours

Two experiments showed the influence of perceptual set on the perception of subjective contours. In the first, the perceived shape of a subjective-contour figure (a minimal version of the Ehrenstein configuration) was varied by altering the observer’s viewing set. The second experiment showed that apparent depth emerged in subjective-contour figures when observers were set to perceive the illusory contours.