TVA-based modeling of data from Experiment 2 revealed that single words are processed significantly faster than letters, whereas the perceptual threshold did not differ between the two types of stimuli. In the third experiment, a classic whole report with multiple stimuli, a different pattern of performance emerged: Processing speed was faster for letters than words.
Our findings indicate that the WSE is more general than previously reported. When presented in isolation, at the center of the visual field, single words are identified better than single letters at all exposure durations between the perceptual threshold and ceiling performance.
However, although single words are perceived and reported better and faster than single letters, words do not enjoy the same advantage when multiple stimuli are presented simultaneously. In such cases, single letters are processed faster than words, and, in addition, more single letters than whole words can be encoded into VSTM.
Also, there is a general decrease in processing speed for both stimulus types from the single item to the whole report experiment.
It is well-known that both errors and RTs increase with eccentricity Eriksen and Schultz, ; Carrasco et al. The WSE has typically been reported in experiments using brief, masked displays of single stimuli e. Our results suggest that this may not be necessary, as the WSE, at least when measured with a report task rather than forced choice, is evident over a range of exposure durations.
Using a two-alternative forced-choice paradigm comparing performance with postmasked words and single letters, Jordan and de Bruijn ; see also Jordan and Bevan, found that word superiority persisted only when the same size masks were used for both words and letters but disappeared when the width of the masks were adjusted to the actual width of the individual stimuli. This latter approach, however, may inadvertently have resulted in a letter benefit as certain letters could easily be excluded just by the size of their masks.
Hence, we used similar masks for both letters and words. Even if the WSE we observed in Experiment 2 could potentially be explained by the mask we used, this does not necessarily make the effect less interesting. Also, mask attributes cannot explain why the effect is reversed in Experiment 3, where the same stimuli and masks were employed.
In addition, the results of Experiment 1 indicate that words are processed more efficiently than single letters even when they are unmasked. Cattell was the first to record such a word superiority in vocal naming times, but the phenomenon has not been studied to any large degree, although it does, in our opinion, deserve further investigation.
For instance, it is possible that some of the word advantage in RTs may have its roots on other levels of processing than in visual perception, and may perhaps be related to the ease of phonological retrieval.
The relative speed of lexical and sublexical processing has been investigated within the framework of the Dual Route Cascaded model of reading Coltheart et al. Sublexical processing letter-sound translation processes is slower than lexical whole word processing, and this may be related to the RT difference we observe between single letters and words.
It may also be the case, however, that the advantage in visual processing speed observed for words compared to letters in Experiment 2 contributes to the overall difference in RT, and this would be interesting to investigate further.
One question that remains is why words—when they are so effectively processed alone—do not enjoy the same advantage when multiple stimuli are presented simultaneously.
Why can our subjects not encode as many words into their VSTM as they can letters? First, this argues against the notion that words are processed as units, or at least as units encodable in VSTM. This is qualified by the finding that capacity decreases as objects become more complex Alvarez and Cavanagh, , which could perhaps explain our finding, as words are obviously more visually complex than single letters.
On the other hand, some studies indicate that VSTM capacity is larger for objects of expertise than unfamiliar objects Curby et al. Being fluent readers, our subjects are indeed experts in word identification, and in that light the limit of their VSTM capacity for words seems surprisingly low.
Another possible explanation of the reversed effect in the whole report experiment is that stimuli were presented outside the central visual field at 4. Jordan and Patching have shown that the word-letter phenomenon can be reversed when stimuli are presented in lateralized displays, which resembles the effect we find in Experiment 3.
They suggest that while crowding effects or effects of lateral masking are counteracted by strong lexical activations when words are presented foveally, such top—down effects do not prevent crowding in lateralized displays. This presents a challenge for our ability to measure the capacity of VSTM for word stimuli, however, as it will be difficult to avoid both within and between stimulus crowding in the same paradigm, while keeping stimuli in the central visual field.
It is worth noticing, however, that if we count the number of letters encoded in the word condition in Experiment 3, we do see a WSE: While our subjects could only encode a mean of 2. This is clearly superior to their performance in the letter condition, where the mean capacity was about four letters.
Thus, the WSE may be said to be present also in the whole report condition, but not to the same extent as in the single item task. We have previously used methods based on TVA to investigate visual processing in the disorder of pure alexia, where word reading is disrupted by brain injury, typically affecting the visual word form area and surrounding structures Starrfelt et al.
We have shown that this seemingly selective reading disorder is characterized by reduced central processing speed not only for letters but also for digits, and reduced VSTM capacity for both types of stimuli. An interesting extension of the current work would be to compare pure alexia patients' performance with words and letters using similar paradigms.
The reading deficit in pure alexia affects both word and letter identification, but yet a WSE words vs. Indeed, in the same patients where we observed reduced central processing speed and VSTM capacity for unrelated letters and digits, we also found better report of letters from words compared with non-words Starrfelt et al.
The word-letter experiments presented in the current paper seem fit to characterize the relationship between letter and word processing in pure alexia further. Pure alexia is thought to be a deficit in parallel processing of letters, resulting in a compensating strategy of serial letter identifications and thus a large effect of word length on reading times. If this is the case, we should expect patients to show the opposite pattern of performance in our single stimulus word-letter experiments compared to normal subjects: they should be slower in naming words than letters, and show reduced processing speed for words compared with letters.
Indeed, if pure alexia truly abolishes parallel letter processing, one would expect their threshold for identifying three letter words to be three times as high as for single letters. We have shown that the WSE, at least for simple short words, can be revealed in vocal reaction times, and that part of this superiority is probably caused by increased visual processing speed for words compared to letters. This fits neatly with previous observations of the WSE, and the interpretation that top—down connections may enhance processing of letters in words, while single letter processing may rely more on bottom-up signals.
A novel finding is that the WSE is significant at a range of exposure durations, which means that at least in our paradigm, the meticulous search for a given performance level is not necessary to reveal the effect. Rather, words seem to be processed better or faster than letters from the threshold of perception. When several stimuli are presented simultaneously, we find the opposite result: letters are processed faster than words, and more letters than words can be encoded in VSTM.
This indicates that words are not treated as units in VSTM. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We are grateful to the Danish Lexicographic Society for creating a list of orthographic neighborhood size N-size for Danish words.
The first author is indebted to CG Fakutsi for keeping the words together, and to an anonymous computer technician in Majori, Italy, for rescuing the data from these experiments. Thanks to Felicia Kettelz and Mark Ruby for testing and data coding. Alvarez, G. The capacity of visual short term memory is set both by visual information load and by number of objects.
Behrmann, M. A literature review and new data supporting an interactive account of letter-by-letter reading. CrossRef Full Text. Bergenholtz, H. Dansk Frekvens Ordbog. Copenhagen: G. Gads Forlag. Bundesen, C.
A theory of visual attention. A neural theory of visual attention: bridging cognition and neurophysiology. Carrasco, M. Visual factors in word perception. McClelland, J. An interactive activation model of context effects in letter perception, part 1: An account of basic findings.
Psychological Review , , Prinzmetal, W. The word superiority effect does not require a T-scope. Reicher, G. Perceptual recognition as a function of meaningfulness of stimulus material. In such cases, single letters are processed faster than words, and, in addition, more single letters than whole words can be encoded into VSTM. Also, there is a general decrease in processing speed for both stimulus types from the single item to the whole report experiment.
It is well-known that both errors and RTs increase with eccentricity Eriksen and Schultz, ; Carrasco et al. The WSE has typically been reported in experiments using brief, masked displays of single stimuli e. Our results suggest that this may not be necessary, as the WSE, at least when measured with a report task rather than forced choice, is evident over a range of exposure durations. Using a two-alternative forced-choice paradigm comparing performance with postmasked words and single letters, Jordan and de Bruijn ; see also Jordan and Bevan, found that word superiority persisted only when the same size masks were used for both words and letters but disappeared when the width of the masks were adjusted to the actual width of the individual stimuli.
This latter approach, however, may inadvertently have resulted in a letter benefit as certain letters could easily be excluded just by the size of their masks. Hence, we used similar masks for both letters and words.
Even if the WSE we observed in Experiment 2 could potentially be explained by the mask we used, this does not necessarily make the effect less interesting.
Also, mask attributes cannot explain why the effect is reversed in Experiment 3, where the same stimuli and masks were employed. In addition, the results of Experiment 1 indicate that words are processed more efficiently than single letters even when they are unmasked.
Cattell was the first to record such a word superiority in vocal naming times, but the phenomenon has not been studied to any large degree, although it does, in our opinion, deserve further investigation.
For instance, it is possible that some of the word advantage in RTs may have its roots on other levels of processing than in visual perception, and may perhaps be related to the ease of phonological retrieval. The relative speed of lexical and sublexical processing has been investigated within the framework of the Dual Route Cascaded model of reading Coltheart et al. Sublexical processing letter-sound translation processes is slower than lexical whole word processing, and this may be related to the RT difference we observe between single letters and words.
It may also be the case, however, that the advantage in visual processing speed observed for words compared to letters in Experiment 2 contributes to the overall difference in RT, and this would be interesting to investigate further.
One question that remains is why words—when they are so effectively processed alone—do not enjoy the same advantage when multiple stimuli are presented simultaneously. Why can our subjects not encode as many words into their VSTM as they can letters? First, this argues against the notion that words are processed as units, or at least as units encodable in VSTM.
This is qualified by the finding that capacity decreases as objects become more complex Alvarez and Cavanagh, , which could perhaps explain our finding, as words are obviously more visually complex than single letters.
On the other hand, some studies indicate that VSTM capacity is larger for objects of expertise than unfamiliar objects Curby et al. Being fluent readers, our subjects are indeed experts in word identification, and in that light the limit of their VSTM capacity for words seems surprisingly low. Another possible explanation of the reversed effect in the whole report experiment is that stimuli were presented outside the central visual field at 4.
Jordan and Patching have shown that the word-letter phenomenon can be reversed when stimuli are presented in lateralized displays, which resembles the effect we find in Experiment 3. They suggest that while crowding effects or effects of lateral masking are counteracted by strong lexical activations when words are presented foveally, such top—down effects do not prevent crowding in lateralized displays.
This presents a challenge for our ability to measure the capacity of VSTM for word stimuli, however, as it will be difficult to avoid both within and between stimulus crowding in the same paradigm, while keeping stimuli in the central visual field. It is worth noticing, however, that if we count the number of letters encoded in the word condition in Experiment 3, we do see a WSE: While our subjects could only encode a mean of 2.
This is clearly superior to their performance in the letter condition, where the mean capacity was about four letters. Thus, the WSE may be said to be present also in the whole report condition, but not to the same extent as in the single item task.
We have previously used methods based on TVA to investigate visual processing in the disorder of pure alexia, where word reading is disrupted by brain injury, typically affecting the visual word form area and surrounding structures Starrfelt et al.
We have shown that this seemingly selective reading disorder is characterized by reduced central processing speed not only for letters but also for digits, and reduced VSTM capacity for both types of stimuli. An interesting extension of the current work would be to compare pure alexia patients' performance with words and letters using similar paradigms.
The reading deficit in pure alexia affects both word and letter identification, but yet a WSE words vs. Indeed, in the same patients where we observed reduced central processing speed and VSTM capacity for unrelated letters and digits, we also found better report of letters from words compared with non-words Starrfelt et al.
The word-letter experiments presented in the current paper seem fit to characterize the relationship between letter and word processing in pure alexia further. Pure alexia is thought to be a deficit in parallel processing of letters, resulting in a compensating strategy of serial letter identifications and thus a large effect of word length on reading times.
If this is the case, we should expect patients to show the opposite pattern of performance in our single stimulus word-letter experiments compared to normal subjects: they should be slower in naming words than letters, and show reduced processing speed for words compared with letters. Indeed, if pure alexia truly abolishes parallel letter processing, one would expect their threshold for identifying three letter words to be three times as high as for single letters.
We have shown that the WSE, at least for simple short words, can be revealed in vocal reaction times, and that part of this superiority is probably caused by increased visual processing speed for words compared to letters.
This fits neatly with previous observations of the WSE, and the interpretation that top—down connections may enhance processing of letters in words, while single letter processing may rely more on bottom-up signals. A novel finding is that the WSE is significant at a range of exposure durations, which means that at least in our paradigm, the meticulous search for a given performance level is not necessary to reveal the effect.
Rather, words seem to be processed better or faster than letters from the threshold of perception. When several stimuli are presented simultaneously, we find the opposite result: letters are processed faster than words, and more letters than words can be encoded in VSTM.
This indicates that words are not treated as units in VSTM. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We are grateful to the Danish Lexicographic Society for creating a list of orthographic neighborhood size N-size for Danish words.
The first author is indebted to CG Fakutsi for keeping the words together, and to an anonymous computer technician in Majori, Italy, for rescuing the data from these experiments. Thanks to Felicia Kettelz and Mark Ruby for testing and data coding. All words are high frequency Danish words, with high neighborhood-size.
At least two neighbor words were included in the list for all stimuli, thus making it necessary to process at least two, and for most words all three letters in the word to identify it correctly. National Center for Biotechnology Information , U. Journal List Front Hum Neurosci v. Front Hum Neurosci. Published online Sep 4. Author information Article notes Copyright and License information Disclaimer.
Received Apr 29; Accepted Aug The use, distribution or reproduction in other forums is permitted, provided the original author s or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. This article has been cited by other articles in PMC. Abstract Words are made of letters, and yet sometimes it is easier to identify a word than a single letter.
Experts have come up with several categories of advantages for letters that are included in a word, rather than a random sequence or even a pseudo-word, such as a brand name. One advantage is that words are pronounceable, which adds an auditory component to the process of memorization. Another is the frequency with which words are used, again, compared to non-word sequences of letters; semantic value is another category of benefit.
The Word Superiority Effect has been useful in the construction of some types of routine testing.
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