Evidence for direct visual access to letter identities

Subjects were presented with two letters from the set BCDFGHLNPORTVZ, one in upper case and one in lower case. Subjects were required to decide, as quickly as possible, whether the two letters on each trial were the same (e.g., Bb) or different (e.g., Bd). Because letters were always physically different, subjects presumably must name the letters in order to respond. Reaction times were predicted by the visual similarity of the letters, and not by their phonemic distinctive feature similarity. Consistent with previous work showing that a word's meaning can be assessed directly from visual information, the findings suggest that visual analysis of a capital or small letter can result in knowing the latter name without further linguistic processing. These results were interpreted as an example of automatic detection as described by Schneider and Shiffrin (1977).     

Detection of letter repetition in words and nonwords: the effect of opposite-case distractors.

This study tested whether it is the repetition of the letter's name and not its shape that is detected faster in a word than in a nonword (Krueger, 1989). Ss judged whether the same letter shape or the same letter name was repeated in a 6-letter word or nonword. When the shape was repeated, the word advantage was nearly as large (about 50 ms) when Ss looked for a physical match as when they looked for a name match. When the 2 repeated letters differed in case, however, the word advantage was very large (208 ms) when Ss looked for a name match and were thus rewarded for nonvisual coding, but the advantage vanished ((-35)-ms word deficit) when Ss looked for a physical match and were thus penalized for nonvisual coding. This indicates that letter names are much more accessible in words than in nonwords, and that words are primarily encoded nonvisually.     

Changes in letter processing in beginning readers

Letter pairs were tachistoscopically presented to children from grades 1, 2 and 6 (85.6, 99.4, and 147.8 months of age, respectively). They were required to determine whether the letters had a same name by pressing one of two response keys as fast as possible. Also a letter detection task was presented where letter matching was either based on physical or name characteristics. The name match in both tasks was slower than the match of letters which shared the same visual form. The name-physical match differences changed significantly as a function of grade level. Shifts in latency differences over grades can be considered as a fundamental correlate of reading ability. Children increasingly employ strategies of processing based on nominal cues and become efficient in extracting the invariant features of letters amongst irrelevant variations such as type face.     

Stimulus probability and same-different classification

Three experiments investigated the effect of stimulus probability on same-different classification time. In Experiments I and II, subjects made same responses on the basis of name matches of simultaneously presented letters. Half of the same trials involved letters that were also physically identical. Experiment I showed that the presentation probability of specific letters affected name matches and different responses, but not physical matches. Experiment II varied stimulus contrast as well as probability. Contrast had a main effect but did not interact with probability at any level of processing. In Experiment III, subjects were switched to the physical level of processing. Stimuli that now had the same name but differed in case were called different. In this condition, the probability effects obs(irved in Experiment II disappeared. These results are interpreted as demonstrating that stimulus probability has its effect during the process that derives the name of the stimulus from the visual representation. This process takes place before the name comparison is made, and the name comparison process precedes the determination of the different response.     

Visual and verbal coding in the interhemispheric transfer of information

A manual response was used to record a decision of ‘same’ or ‘differ’ on two visual signals which were presented simultaneously, either both to the same hemisphere or each to different hemispheres. The signals were drawn from the set of letters A, B, a, b. Eight subjects were required to match on the basis of the names of the letters (irrespective of whether they were capitals or lower case) and eight subjects were required to match on the basis of the visual identity of the signals.Reaction times were measured for ‘same’ and ‘differ’ decisions.This experiment extends a previous study by the same authors (Davis and Schmit 1971). The previous finding, that when two signals are presented each to different hemispheres, reaction times are shorter than when both are presented to the same hemisphere, was confirmed for both visual and name matching. New evidence is provided on the role of each hemisphere in the analysis and comparison of signals, on either a visual or a verbal basis, for ‘same’ and ‘differ’ decisions. A model to explain the results in terms of the different functions of the two hemispheres is proposed.     

Automatic letter priming in an alphabetic decision task

An alphabetic decision task was used to study effects of form priming on letter recognition at very short prime durations (20 to 80 msec). The task required subjects to decide whether a stimulus was a letter or a nonletter. Experiment 1 showed clear facilitatory effects of primes being either physically or nominally identical to the targets, with a stable advantage for the former. Experiment 2 demonstrated that uppercase letters are classified more rapidly as letters (vs. non-letters) when they are preceded by a briefly exposed, forward- and backward-masked, visually similar uppercase letter than when they are preceded by a visually dissimilar uppercase letter. Finally, Experiment 3 demonstrated that nominally identical and visually similar primes facilitate processing more than do nominally identical, visually dissimilar primes. The alphabetic decision task proved to produce sensitive and stable priming effects at the feature, letter, and response-choice level. The present results on letter-letter priming thus constitute a solid data base against which to evaluate other priming effects, such as word-letter priming. The results are discussed in light of current activation models of letter and word recognition and are compared with data simulated by the interactive activation model (McClelland & Rumelhart, 1981).     

Recognition vs recall of visually vs acoustically confusable letter matrices

In an attempt to separate auditory and visual components in short-term memory, five subjects were exposed to letter matrices composed of six visually confusable letters, six acoustically confusable letters, or a mixture of the two, under two response conditions: recognition and recall. A 50-msec stimulus presentation was followed by a variable dark interval of 1, 250, 1,000, or 3,000 msec. In the recall condition, the interval was followed by a buzzer which signaled the subject to recall, in any order, as many letters as possible. In the recognition condition, the variable interval was followed by a second letter matrix which was either identical to the first matrix or differed from is by one letter. Subjects responded either "same" or "different." The results support the notion that the auditory component plays a major role in recall, whereas the visual component dominates in recognition.     

Are nominal same-different matches slower due to differences in level of processing or to response competition?

Eriksen, O’Hara, and Eriksen (1982) have proposed that the latency advantage ofsame overdifferent judgments when the match is based upon physical identity is due to differential amounts of response competition between the responses by which the judgment ofsame ordifferent is signified. Responses of “different” are slowed by a high level of priming in the competing response signifyingsame. In the present experiment, the response competition model is extended to nominal matches and in particular to what Proctor 1198D has termed the “name-physieal disparity”—a pair of letters are more rapidly judged to have the same name if they are the same ease (e.g., a a) than if they are in different eases (e.g., A a). While response competition effects were found to occur in nominal matches of this kind, the name-physieal disparity was greater than could be attributed solely to response competition. Evidence was obtained that part of the name-physieal disparity could be attributed to the subject’s having two chances to make a-nominal raatch when the letter pair was identical both physically and in name. The match could be made either on the basis of the physical or the name code. It was assumed that name and physical codes were processed at least partially independently.     

Hemisphere-specific processes in letter matching

Three experiments were designed to investigate outstanding questions concerning the effect of memory load variations on efficiency and coding processes in the left and right cerebral hemispheres. In Experiment 1 subjects were presented with one, two, or three target letters in uppercase or lowercase in central vision, followed by simultaneous bilateral probes requiring a name match response. Twenty young right-handed adults, 10 males and 10 females, acted as subjects. Two main features of the results were as follows: (a) The slope of the linear function relating mean reaction time (RT) and set size was 30% greater for right visual field (RVF)-left-hemisphere probe stimuli under both physical and name identity conditions, and (b) RT for RVF-left-hemisphere probes was greater when the probe was drawn from preterminal serial position in the target list. Experiments 2 and 3 examined the proposition that the results of Experiment 1 reflected asymmetric interference during list acquisition. The results showed that, first, the LVF-right-hemisphere advantage was eliminated or reversed under unilateral probe presentation conditions, and second, the LVF-right-hemisphere advantage for a single, preterminal serial position was insensitive to variations in the interitem interval. The results are thought to be inconsistent with the interference hypothesis. The general implications of the results for existing theories of hemisphere function are discussed.     

A unilateral field advantage for detecting repeated elements

Previous studies have shown that letter repetitions are detected more rapidly when presented bilaterally (one letter in each visual field) than when presented unilaterally (both in the same field) when subjects have to report matches independently of case or font (e.g., Aa). This pattern of results is referred to as a bilateral field advantage. Here, we present evidence of an opposite pattern of results for detecting repeated items when they are physically identical. In our repetition detection paradigm, subjects indicated whether there was a repetition of any two of four presented items, one in each quadrant of the visual field. Stimulus classes tested included letters, color, size, orientation, and motion paths. The subjects were significantly faster at detecting unilateral versus bilateral repetitions for four out of the five stimuli classes tested, with a trend in the same direction for the fifth. This unilateral field advantage suggests that low-level processes group physically identical items more efficiently within hemifields than across.     

Interference with short-term visual memory produced by concurrent central processing

Double-letter memory and test stimuli were used in two experiments on a speek comparison task. Faster decision times were found when memory and test stimuli were physically identical than when they were the same in name only. This finding was true even with retention intervals as long as 12 sec and even when difficult tasks filled the retention intervals. However, the decision-time advantage of physically identical comparisons was greatest when the interval was not filled with a task likely to interfere with rehearsals. High verbal subjects had a smaller advantage for the physically identical comparisons than did low verbal subjects but were affected in the same way as low verbal subjects in terms of which conditions raised the overall correct comparison times, raised the error rates, and reduced the advantage of physically identical comparisons.     

Using visual codes for comparisons of pictures

In two experiments, Ss indicated for a series of trials whether or not two pictures of common objects had the same name (a positive or negative response, respectively). The pictures were separated by one of three interstimulus intervals (ISis), and reaction time (RT) was recorded. In Experiment I, positive trials involved pictures that were identical (identity match), mirror images (mirror match), or physically different but had the same name (name match). The stimuli came from either an S set, in which name-match pairs were physically similar, or a D set, in which name-match pairs were physically dissimilar. The mean RTs for mirror and identity matches were virtually the same but faster than name-match RTs, an advantage that decreased with increasing ISI. It was expected that name-match RT for the S set would be less than for the D set, indicating a facilitative effect of physical similarity; however, the identity-match RTs showed the expected difference. These results were extended in Experiment II, which involved only the identity and name matches, in pure sessions (which included positive trials of just one type) or mixed sessions (which included both types of positive trials). For mixed sessions, name- as well as identity-match RTs differed between the S and D sets. These results provide evidence for the use of visual codes in comparing nonidentical pictures, codes that apparently vary with experimental context and task demands.     

Reaction times and evoked potentials as indicators of hemispheric differences for laterally presented name and physical matches

Letter pairs, which could be name matches, physical matches, or mismatches, were presented at fixation or 2.5 degrees left or right of fixation. During different experimental sessions, the locations and the types of matches were fixed (and therefore known in advance by the subject) or were randomized. Right visual field superiority in reaction time occurred for name matches only when location was randomized, and then the extent of the superiority depended on whether the types of match called for were predictable. Evoked potentials to the letter pairs during this task revealed hemispheric and neural pathway differences that were independent of expectancy condition. Right hemisphere responses were larger than left. For some components, amplitudes were smaller and latencies were shorter for direct than for indirect projection of stimuli to each cerebral hemisphere. Indirect-direct differences in P300 amplitude varied for each cerebral hemisphere according to whether a physical or name match occurred. The P130 and N170 components manifested hemispheric differences that depended on whether the two letters of a pair were in the same or different cases.     

Memory of a speaker's voice: Reaction time to same- or different-voiced letters

Subjects were presented with a sequence of two letters, each letter spoken in either a male or female voice. On each trial, the subject was required to indicate, as quickly as possible, whether the two letters had the same name. Reaction times (RTs) were faster for letters spoken in the same voice for both “same” and “different” responses, even when letters were separated by 8 s. These results are incompatible with the notion of physical and name codes in auditory memory since a “different” response should always be based on a comparison of letter names and should not be influenced by voice quality. It was also found that RTs were not influenced by the phonemic distinctive feature similarity of the letters.     

Search for a matching or mismatching letter pair

The perceptual matching task was modified in order to increase the error rate and thus to reveal more clearly whether internal noise more often changes an objective match into a perceived mismatch than vice versa (noisy-operator theory). In Experiment 1, subjects searched for a “same” pair in a list of “different” pairs or for a “different” pair in a list of “same” pairs. As predicted, the target pair was overlooked or missed more often on “different” lists. False alarms, though, were not higher on “same” lists, owing apparently to rechecking, which also produced slower search through “different” lists. To disable the rechecking mechanism, rapid serial visual presentation (RSVP) was used in Experiments 2 and 3. As predicted, misses exceeded false alarms on “different” lists, whereas the reverse held on “same” lists, both at the physical level (Experiment 2) and at the name level (Experiment 3). Letter set size and repetition were varied in Experiments 1 and 2, and the results indicate that when letter pairs are presented in close temporal and spatial proximity, subjects are influenced by extraneous interpair comparisons in addition to relevant intrapair comparisons in deciding whether or not a target pair is present.     

Speed of letter cancellation on the basis of visual and name identity in young children

Second-, fourth-, and sixth-grade children were tested on a visual search task where letter matching was based on the visual or name characteristics of letters. Visual match lists were searched faster than name match lists by all three grades. In the name match lists there was an increase in speed as a function of trials whereas in the visual match lists there was no increase. The name-physical match difference did not change as a function of age.     

Same—differentjudgments of multiletter strings: Insensitivity to positional bias and spacing

Several recent studies of multiletter matching have included pairs of strings that have-the-same letters in different positions (rearranged pairs). The task can be defined such that these rearranged pairs are correctly classified asdifferent (i.e., subjects respond “same” only if the strings have the same letters in the same positions—the order task) or assame (i.e., subjects respond “same” if the strings have the same letters regardless of their positions—the item task). The order task produces left-to-right serial-position effects, whereas the item task produces U-shaped serial position effects. Because these differences suggest that subjects may be able to exert strategic control over the comparison process, two sets of experiments were designed to test whether or not subjects can change the relative weightings devoted to the respective serial positions. In Experiments 1 and 2, the probability that a mismatch occurred in the different positions was manipulated. In Experiments 3 and 4, the physical spacing between letters, as well as whether or not the spaces were filled with neutral noise characters, was varied. None of the manipulations had much influence on the serial-position effects. Thus, the distinct serial-position effects for the order and item tasks apparently are mandatory and not due-to-any voluntary-comparison strategy.     

Is visual image segmentation a bottom-up or an interactive process?

Visualimage segmentation is the process by which the visual system groups features that are part of a single shape. Is image segmentation a bottom-up or an interactive process? In Experiments 1 and 2, we presented subjects with two overlapping shapes and asked them to determine whether two probed locations were on the same shape or on different shapes. The availability of top-down support was manipulated by presenting either upright or rotated letters. Subjects were fastest to respond when the shapes corresponded to familiar shapes—the upright letters. In Experiment 3, we used a variant of this segmentation task to rule out the possibility that subjects performed same/different judgments after segmentation and recognition of both letters. Finally, in Experiment 4,we ruled out the possibility that the advantage for upright letters was merely due to faster recognition of upright letters relative to rotated letters. The results suggested that the previous effects were not due to faster recognition of upright letters; stimulus familiarity influenced segmentation per se. The results are discussed in terms of an interactive model of visual image segmentation.     

The time course of visual influences in letter recognition

This study builds on a specific characteristic of letters of the Roman alphabet—namely, that each letter name is associated with two visual formats, corresponding to their uppercase and lowercase versions. Participants had to read aloud the names of single letters, and event-related potentials (ERPs) for six pairs of visually dissimilar upper- and lowercase letters were recorded. Assuming that the end product of processing is the same for upper- and lowercase letters sharing the same vocal response, ERPs were compared backward, starting from the onset of articulatory responses, and the first significant divergence was observed 120 ms before response onset. Given that naming responses were produced at around 414 ms, on average, these results suggest that letter processing is influenced by visual information until 294 ms after stimulus onset. This therefore provides new empirical evidence regarding the time course and interactive nature of visual letter perception processes.     

Interactions among levels of processing

This article examines associations among representations of physical, name, and category information by determining effects of category repetition on and following physical, name, and category match trials. Subjects decided whether two letters were from the same half of the alphabet. Category repetition effects were evidenced by faster ~nd more accurate responses when letters from the same half of the alphabet were used on successive trials. Although physical matches showed no effect of category repetition, name and category matches did. Trials following physical matches were less affected by category repetition than were trials following name or category matches. The results suggested that these category repetition effects were mediated by interletter associations: Reaction time increased with the alphabetic distance between preceding and current letters. However, these distance effects held only for forward (A → B) and not backward (B → A) alphabetic sequences, suggesting that the alphabetic representation is ordinal and unidirectional.