Category-level contributions to the alphanumeric category effect in visual search

Do letter and digit recognition depend on the same or different cognitive mechanisms? Letters are detected more quickly among digits than among letters; likewise, digit search is facilitated when distractors are letters, as opposed to digits. This effect suggests that different mechanisms underlie recognition of these two categories. There are, however, systematic physical differences between letters and digits that might account for the effect. We used target and distractor stimuli that facilitated within-category search when inverted, and category identity was, thereby, attenuated. However, in conditions of upright search, in which category identity was more salient, between-category search was more efficient for the same stimuli. These findings suggest that letter and digit recognition are, at least to a degree, functionally independent.     

Recognition time for letters and nonletters: effects of serial position, array size, and processing order

Three experiments address the question of whether end-effects (the advantage for the first and last letters in multi-letter arrays) are due to sensory or cognitive factors. The basic strategy used was to compare letters with symbol stimuli that do not lend themselves to top-down processing. Serial position functions using central fixation were obtained in the first experiment for letters, digits, and symbols. End-effects were present with both letters and digits, indicating that processes limited to word recognition cannot be responsible for end-effects. Five-symbol arrays, however, yielded U-shaped reaction time functions, with poorest performance at the initial and terminal positions. The effects of array size and retinal placement were investigated with letters and symbols in a second experiment. Multi-letter and symbol arrays differed primarily in that letters showed end-effects that were independent of retinal placement, whereas symbols did not. The conclusion that multi-letter and symbol arrays are not processed in the same way was tested in a third experiment. Using a paradigm that eliminated processing order as a variable, the experiment obtained identical effects of ordinal position within an array for letters, digits, and symbols. It is concluded that sensory factors cannot provide a viable account of letter end-effects and that letter and nonletter comparisons can improve our understanding of the sensory and cognitive factors involved in letter perception.     

Display vs. memory search for digits and faces among mentally handicapped and MA-matched non-handicapped youngsters

This experiment was designed to explore possible explanations for handicapped individuals' characteristically poor performance on memory scanning tasks. Independent variables included group (mentally handicapped vs. non-handicapped), type of search (display vs. memory), type of stimuli (digits vs. pictures of unfamiliar boys' faces), and load (2, 3, or 4 items to be searched). Results indicated that handicapped and non-handicapped groups did not differ when searching displays but did when searching memory, which suggested that the handicapped group's most significant impairment was specific to some aspect of memory search. Handicapped youngsters were also hindered by increasing loads more than control youngsters were. This result as well as impairment in memory search may have been due to handicapped youngsters' relatively short visual spans. The groups did not differ in their response to the two types of stimuli, faces and digits. Facial search was a considerably more demanding task than digit search for handicapped and normal children.     

Processes underlying long-term repetition priming in digit data entry

Two experiments examined long-term repetition priming in data entry. In each experiment, participants entered 4-digit numbers displayed as either words or numerals, and responded with digits (Experiment 1), or either digits or initial letters (Experiment 2). At test 1 week later, they entered old and new numbers, with the format changed for half of the old stimuli. Implicit memory was evidenced at test by faster entry of the old than the new numbers, regardless of whether the numbers were in the same or different format, suggesting that the abstract numerical meaning, not the surface form, contributes to repetition priming. Numbers presented as words in training had an advantage over numbers presented as numerals, regardless of response format, implying that type of processing also contributes to the effect and ruling out an explanation based on time spent processing numbers in word format.     

Effects of type of responding on memory/visual search: Responding just “yes” or just “no” can lead to inflexible performance

Interactions of stimulus consistency and type of responding were examined during perceptual learning. Subjects performed hybrid memory-visual search tasks over extended consistent and varied mapping practice. Response conditions required subjects to respond to both the presence and absence of a target, only when a target was present or only when a target was not present. After training, the subjects were transferred to a different response condition. The results indicate that: (1) performance on search tasks with stimuli that are variably mapped show no qualitative changes attributable to manipulation of response format; (2) improvement due to consistent mapping (CM) practice is attenuated in the no-only response condition; (3) yes-only CM training attenuates the subjects ability to transfer to no-only responding; and (4) yes/no CM training leads to the greatest improvement and transfer when compared with other responding conditions. The practice and transfer data support and extend previous research investigating effects of response set in memory/visual search and help to delineate factors that facilitate or inhibit reduction of load effects in memory and visual search.     

Transfer of stimulus differentiation and perceptual selection rules

Three experiments examined the conditions under which transfer of stimulus differentiation occurs. Two experiments involved transfer in paired associate lists having identical stimuli and re-paired response terms compared with lists having different stimuli. In one experiment, transfer was determined for lists of three-word stimuli in which various elements were shared among the stimuli. The pattern of redundancy was such that the spatial position of a discriminative element was either consistent or not consistent in different items, or there was no discriminative element. Transfer of differentiation was obtained only when position was constant. In the second experiment, stimuli were single words and were either unrelated, rhymed, or were instances of common concepts. No evidence of transfer of differentiation was obtained with either rhymes or concepts. In the third experiment, subjects learned pairs in which the stimuli were single letters; then subjects transferred to a list in which either rhyming or unrelated stimuli began with the same letters. Transfer was not differential.     

Categorization and identification of simultaneous targets.

Early and late selection theories of visual attention disagree about whether identification occurs before or after selection. Studies showing the category effect, i.e., the time to detect a letter is hardly affected by the number of digits present in the display, are taken as evidence for late selection theories since these studies suggest parallel identification of all items in the display. As an extension of previous studies, in the present study two categorically different targets were presented simultaneously among a variable number of nontargets. Subjects were shown brief displays of two target letters among either 2, 4 or 6 nontarget digits. Subjects responded 'same' when the two letters were identical and 'different' otherwise. Since the 'same-different' response reflects the combined outcome of the simultaneous targets, late-selection theory predicts that the time to match the target letters is independent of the number of nontarget digits. Alternatively, early-selection theory predicts a linear increase of reaction time with display size since the presence of more than one target disrupts parallel preattentive processing, leading to a serial search through all items in the display. The results provide evidence for the early-selection view since reaction time increased linearly with the number of categorically different nontargets. A control experiment revealed that none of the alternative explanations could account for the display size effect.     

Perceptual selectivity is task dependent: The pop-out effect poops out

An attempt was made to determine why evidence for perceptual selectivity based on conceptual category (e.g., digits vs. letters) has been found in some experiments but not in others. Experiments using the partial-report paradigm find no partial-report superiority when the report is cued by category, whereas, in recent visual search studies, evidence for perceptual selectivity has been obtained for arrays containing a single item that was categorically different from the other items (e.g., a digit among letters). Using a search task, Experiment 1 investigated the possibility that the number of categorically different items in the arrays could be a determinant of selectivity. One, two, or three digits and a variable number of letters were presented on each trial, and subjects determined if a particular digit was present. No evidence of selectivity was obtained, even for the one-digit condition. Experiment 2 verified this result, and Experiment 3 extended the failure of selectivity to a search task in which the possible targets differed in color from the distractor items. In Experiment 4, subjects counted the number of digits or red letters in arrays in which black letters were the distractor items. The counting task was used to eliminate the requirement in our previous tasks that the subjects search forspecific items. Evidence was obtained in the counting task for selectivity based on the color difference but not on the categorical difference. The color stimuli used in the counting task were essentially the same as those that did not yield any evidence of selectivity in the search task. The results suggest that task demands are an important determinant of whether or not perceptual selectivity will occur.     

The effect of an extraneous added memory set on item recognition: A test of parallel-dependent vs. serial-comparison models

The linear increase in response time (RT) in item recognition as a function of memory set size may be attributed either to increased memory search, as in Sternberg’s serial-comparison model, or to increased interference and competition for a limited processing capacity, as in a parallel-dependent model. An additional memory load was imposed on the normal item recognition task. If the normal task involved letters, the additional task involved digits, or vice versa. The added set was presented before and tested after the normal core set was presented and tested. Across the four trial blocks, the subjects did come to dissociate the two memory sets, but this could be due as much to directed rehearsal as to directed search when other results, including the subjects’ postsession reports, are considered. Other findings, such as the higher error rate and shorter RT for positive than negative trials, seem to reflect differences in effective trace strength, and thus are consistent with the parallel-dependent model.     

Efficiency of visual selection in duplex and conjunction conditions in partial report

Factors that determine the efficiency of visual selection were investigated in two precued partial-report experiments. There were four selection conditions: acolor condition (e.g., selecting purple letters among blue letters), aclass condition (e.g., selecting letters among digits), aduplex condition (e.g., selecting purple letters among blue digits; that is, the targets differed from the distractors both in color and in alphanumeric class), and aconjunction condition (e.g., selecting purple letters among blue letters and purple digits; that is, the targets differed from the distractors either in color or in alphanumeric class). The efficiency of visual selection was highest in the duplex condition and lowest in the conjunction condition. Thedifference in performance across the different selection conditions within subjects was accounted for by variation in the value of a single parameter of the fixed-capacity independent race model (FIRM) proposed by Shibuya and Bundesen (1988), which assumes independent parallel processing, limitations in both processing capacity and storage capacity, and time-invariant selectivity. By assuming that the factors that determine the efficiency of selection in the color and class conditions also underlie the efficiency of selection in the duplex and conjunction conditions, an extension of FIRM, FIRM⁺, accounted for therelationship with respect to efficiency of selection among the different conditions.     

Partially selective search of memory for letters and digits

Three experiments failed to provide evidence that subjects could search just the digits, or just the letters, of a mixed list of digits and letters in deciding whether a probe item was a member of the list. Providing a precue as to the category of the probe shortly before the presentation of the probe decreased the time needed to encode it, but did not change the memory search process. Repeating the category of the probe from one trial to the next, however, did change the pattern of memory search. A "partially selective search" model was proposed which claimed that a mixed list was stored as two categorized sublists, and that a self-terminating search of the sublists could occur in which the first sublist searched was the one which had been probed on the previous trial.     

Automaticity and the detection of speech

The development of automatic perceptual responses to speech stimuli was examined. In the first experiment, phoneme-monitoring performance for speech syllables was examined under conditions in which stimulus-to-response mapping and memory load were manipulated. The results indicated that automaticity develops under consistent-mapping conditions. In the second experiment, a dual-task procedure was combined with mapping and selective attention manipulations in order to examine the development of automaticity across single- and multiple-channel conditions. The results indicated that performance under consistently mapped training conditions was interfered with by dividing attention across multiple channels of input. It is concluded that there may be differences in the way that automaticity develops across visual and auditory modalities and that these differences need to be examined more closely.     

What makes targets redundant?

Two letter-classification experiments that investigated target-redundancy effects on reaction time (RT) were conducted. Both experiments were replicated with choice reaction time (CRT) and go/no-go (GNG) procedures. In each experiment, there were two single-target conditions, one with a noise letter and one without. In one experiment, the letter classes were two letters that could be of either case. In the second experiment, each class consisted of two different capital letters. In both experiments, there were two redundant-targets conditions, one with identical targets and one with the different members of a class. In both of the GNG experiments, redundancy gains were obtained comparing the different-targets condition with the no-noise, single-target condition. Redundant stimuli are ones that lead to the same response. Visually different stimuli may be processed in parallel and jointly activate a response. GNG procedures are more sensitive than CRT in the investigation of redundancy effects.     

What makes targets redundant?

Two letter-classification experiments that investigated target-redundancy effects on reaction time (RT) were conducted. Both experiments were replicated with choice reaction time (CRT) and go/no-go (GNG) procedures. In each experiment, there were two single-target conditions, one with a noise letter and one without. In one experiment, the letter classes were two letters that could be of either case. In the second experiment, each class consisted of two different capital letters. In both experiments, there were two redundant-targets conditions, one with identical targets and one with the different members of a class. In both of the GNG experiments, redundancy gains were obtained comparing the different-targets condition with the no-noise, single-target condition. Redundant stimuli are ones that lead to the same response. Visually different stimuli may be processed in parallel and jointly activate a response. GNG procedures are more sensitive than CRT in the investigation of redundancy effects.     

Aging and the Development of Automaticity in Feature Search

A training experiment was conducted to investigate age differences in the learning that occurs when observers search for an orientation-defined target among a homogeneous set of distractors (i.e., feature search). Eighteen young (M age = 26 years) and seventeen old (M age = 62 years) participants completed seven practice sessions (3,024 trials), followed by a single session of full reversal. Training involved consistent mapping, varied mapping, or nonsearch, in which a precue predicted the target location with 100% validity. Younger and older observers demonstrated equivalent learning rates and equivalent disruption following reversal in all training conditions. Results are interpreted within models of visual attention and search.     

Dichhaptic hand-order effects with verbal and nonverbal tactile stimulation

The palms of normal right-handed subjects were stimulated dichhaptically, i.e., with competing, bimanually presented tactile stimuli consisting of pairs of letters, pairs of digits, or pairs of line orientations. The subjects were required to identify both stimuli in a particular order, and order of report was compared between hands and across stimulus materials. Results indicated right-hand superiority for letters and left-hand superiority for lines; no hand differences occurred for digits. However, observed differences between hands appeared with second reports only, suggesting that measures of tactile storage are more sensitive to laterality differences than measures closer in time to actual stimulation.     

Acquisition process of typing skill using hierarchical materials in the Japanese language

In the present study, using a new keyboard layout with only eight keys, we conducted typing training for unskilled typists. In this task, Japanese college students received training in typing words consisting of a pair of hiragana characters with four keystrokes, using the alphabetic input method, while keeping the association between the keys and typists’ finger movements; the task was constructed so that chunking was readily available. We manipulated the association between the hiragana characters and alphabet letters (hierarchical materials: overlapped and nonoverlapped mappings). Our alphabet letter materials corresponded to the regular order within each hiragana word (within the four letters, the first and third referred to consonants, and the second and fourth referred to vowels). Only the interkeystroke intervals involved in the initiation of typing vowel letters showed an overlapping effect, which revealed that the effect was markedly large only during the early period of skill development (the effect for the overlapped mapping being larger than that for the nonoverlapped mapping), but that it had diminished by the time of late training. Conversely, the response time and the third interkeystroke interval, which are both involved in the latency of typing a consonant letter, did not reveal an overlapped effect, suggesting that chunking might be useful with hiragana characters rather than hiragana words. These results are discussed in terms of the fan effect and skill acquisition. Furthermore, we discuss whether there is a need for further research on unskilled and skilled Japanese typists.     

Controlled and automatic processing during mental rotation

In two experiments, 9- and 10-year-olds and adults were tested on a mental rotation task in which they judged whether stimuli presented in different orientations were letters or mirror-images of letters. The mental rotation task was performed alone on 48 trials and concurrently with a memory task on 48 additional trials. The concurrent memory task in Experiment 1 was recalling digits; in Experiment 2, recalling positions in a matrix. The key result was that the slope of the function relating response time to stimulus orientation was the same when the mental rotation task was performed alone and when performed concurrently with the memory task. This result is interpreted as showing that mental rotation is an automatic process for both children and adults.     

Automatic attraction of attention to former targets in visual displays of letters

Shiffrin and Schneider (1977, Experiment 4d) reported that after consistent training in search for particular alphanumeric characters, presentation of one of these characters (former targets) as a distractor impeded detection of simultaneously presented current targets. Even if presented in an irrelevant display location, the former target appeared to attract attention. Here, we analyze weaknesses in the design of Experiment 4d and report four follow-up experiments ranging from a fairly close replication of the original multiframe experiment to a rather conventional single-frame search study. In each experiment, presentation of former targets consistently impeded detection of simultaneously presented current targets. The results suggest that automatic attention attraction to individual alphanumeric characters develops not only in the special experimental paradigm used by Shiffrin and Schneider, but also in standard visual search tasks. The fact that attention appeared to be attracted by shapes as complex as individual letters supports the assumption that simultaneously presented visual stimuli can be compared in parallel against memory representations of alphanumeric characters.     

Adult counting is resource demanding

Several recent studies on both the development of counting and working‐memory span tasks have provided results that could be interpreted as ruling out any cognitive resource model for counting. The aim of this study was to test the hypothesis that, even in adults, counting is a demanding task that requires the allocation of cognitive resources. In a first experiment, we asked adults to count arrays of dots while maintaining 5 items in memory (either digits or letters). As we predicted, the concurrent memory load did not increase the rate of errors but induced longer counting times. In a second experiment, we asked adults to count using either the numeric chain or the alphabet while they maintained 1, 3 or 5 items in memory (digits or letters). First, we replicated the load effect observed in Experiment 1. Second, though both types of counting required similar amounts of time, counting with the less automatized chain (i.e. the alphabet) resulted in a poorer recall performance. Finally, this detrimental effect in recall was all the more pronounced the greater the number of items to be recalled. These results are interpreted within theoretical frameworks that consider cognitive resources as attentional capacities.