Basic issues in visual perception for language
المؤلف:
Paul Warren
المصدر:
Introducing Psycholinguistics
الجزء والصفحة:
P109
2025-11-05
23
Basic issues in visual perception for language
We have seen that speech perception involves some pre-linguistic analysis of the auditory input, the precise details of which vary according to the model of perception. In visual perception for language, some sort of pre liminary analysis of the input is also assumed to take place. The whole word-shape is probably important, as shown by the fact that we can recognise words containing misspellings or ordering errors, jsut as long as the overoll shape of the word is relatively unaffected. This can even result in errors remaining undetected. For instance, if you have been reading this paragraph quickly, for meaning rather than to identify the detail of every word, you might not have noticed the misspellings of s and o eall two sentences ago. It seems that the visual input is not recognised on a straightforward letter-by-letter basis. This is shown by the word superiority effect. This is the finding that individual letters e.g. are recognised more rapidly and reliably when they occur in words e.g. in WOR than when they are either in nonwords legitimate sequences of letters that happen not to make a word, as in WRO or in jumbled letter strings WLO. Nevertheless, individual letters and letter shapes are important in visual perception for language, and form an important part of approaches to visual
word recognition see Chapter 9. It has also been argued that letter features are significant. Letter features might include horizontal and vertical lines as in H, sloping lines in M, various loops P, p, B and so on. Evidence for the importance of letter features comes from studies that show that it is more difficult to find a letter if it is embedded in a set of letters with similar features.
The specific nature and level of detail that is claimed to be important in the initial visual analysis varies according to the particular theory of perception. It may also depend on the automaticity of visual word recognition, which varies with reading experience.
Stages during visual perception
It is generally assumed that there are stages in the visual perception of language. The initial visual analysis transfers the input into some sort of buffer. This is followed by further analysis in working memory, and then by integration of the analysed input with the linguistic and cognitive interpretation of the text.
Evidence for these stages comes from a number of sources. As we will see below, reading normally proceeds by means of a series of eye fixations, where different portions of text are in the visual field. Although these fixations are relatively brief, at around 250 msec, they are actually longer than is needed to recognise a word. We know this because studies that use very brief presentations of words show that we only need to see a word for about 50 msec in order to be able to recall it quite well. It seems that we fixate on a stretch of text for longer than this because it takes longer to transfer information from a Visual buffer into working memory. This was demonstrated in some early experiments where participants were asked to report which letter in a series of letters had been marked by having a vertical line placed next to it Sperling, 1960. The letters were presented very briefly, and could be recognised from such a brief presentation. The vertical mark was not presented simultaneously with the letters, but after a very short delay. The experience for the participants, though, was that the mark appeared at the same time as the letters, and so they were able to report accurately which letter was marked. But this only happened if the interval between the letters and the vertical mark was not too long. The interpretation of these results is that it takes a short while to transfer information from the visual buffer to working memory, where further processing can take place. If further visual input is received too soon, then the first lot of visual information is added to or overwritten, resulting in the marking of a letter. It follows therefore that if the eyes skip ahead too soon during reading, then the visual information relating to one set of words will be merged with or replaced by the information relating to the next fixation, before it can be shuffled into working memory.
Eye movements during reading
It is clear that the initial visual analysis of text is different from other kinds of visual perception. There are some obvious differences between text and much other visual input, such as the fact that text is generally stationary and can easily be looked at again, text is usually sharply defined but two-dimensional, and so on. There are some important differences in how text is read, compared with other visual processing. An obvious external indication of this can be gained by comparing people’s eye movements when reading text and when watching someone walking across a room. The following summary of eye movements during reading is based on Rayner and Balota (1989). (See also Balota, Yap, & Cortese 2006).
During reading, eye movements are characteristically not smooth, but demonstrate sequences of fixations and saccades jumps. Most of the time readers’ eyes are not in fact moving, since the fixations last about 250 msec while the saccades are very quick, taking between 10 and 20 msec. Each jump moves the eyes forward by approximately 8--9 characters, as shown by the example in Figure 7.5, although the size of the jump can depend on the complexity of the text. The example in the figure is based on data from reading studies using precision cameras that measure the movements of the eyes. It shows three consecutive fixations on a piece of text, and illustrates the information that is available during each fixation.
As indicated by the key in the figure, WI shows that word identification can take place for the words in question, i.e. those at or near the fixation point. BL indicates that the beginning letters of following words can be identified, and LF shows that some of the letter features of the next few letters are discernible. WL means that the reader can judge the relative lengths of words to the right of the fixation point. The solid vertical lines show the total perceptual span of the fixation, which is clearly greater than the size of the jump between fixations, and includes more words than the ones that can be readily identified. The span also takes in more information to the right of the fixation point than to the left. These aspects of the perceptual span during reading have been measured in tasks controlling the amount and nature of information available on screen as a reader progresses through a text, and assessing the impact on the speed and success of reading that results from changing the available information.
The look-ahead evident in Figure 7.5 plays an important part in reading. Being able to tell the difference between shorter and longer words using the word length information marked by WL in the figure helps the reader to distinguish function and content words the former tend to be quite short and to determine which words should be the landing point for the next fixation. Identification of the beginning letters of words BL and some of the letter features in the rest of the word LF allows the lexical search to be started before the word itself is looked at more closely during a subsequent fixation.
This preview effect is one of many factors that influence fixation times and jump distances during reading. Others include the difficulty of the text, the predictability of the fixated words from the prior context, how frequent the words are and how recently they have been encountered, whether the words are ambiguous, and whether there is any priming of the words by previous mention of related words or other material see Chapters 8 and 9 for further discussion of some of these parameters in the context of word recognition.
The nature of the input
It is important to note at this point that languages do not all use the same writing system as English, and that many of the differences between writing systems will have consequences for the visual perception of words or for their recognition. The following are some of the differences. First, there is a range of orthographic writing systems, i.e. of writing systems that represent some aspect of the sounds of words. As we will see in Chapter 9, pronunciation plays a role during reading, and so the relationship between letters and sounds is important. English uses an alphabetic system, but one in which there are many irregularities in the correspondences between letters and sounds. For instance, <c> has a /s/ pronunciation in cease, but a /k/ pronunciation in cat. Languages with a high degree of irregularity are said to have a deep orthography. They contrast with languages in which there is a reasonably direct letter-sound correspondence, and therefore a shallow orthography, such as Italian, Serbo-Croatian or Māori, as well as with languages in which the pronunciation of a particular letter string is reasonably predictable but where there may be many letter strings with the same pronunciation e.g. French, in which the spellings <o>, <au>, <aux>, <eau>, <eaux> can represent the same sound.
Other orthographic writing systems include consonantal systems, such as Hebrew and Arabic, in which the letters often represent the consonants only, and syllabic systems, such as Kannada and the Japanese kana writing system, in which each orthographic symbol represents a syllable. Looking beyond orthographic systems, we find ideographic systems, such as in Chinese, where a symbol corresponds to a word or a portion of a word in a morphologically complex form; with the exception of diacritic markers, the symbol does not bear a direct representation of the sounds of the word.
The range of different writing systems and of the relationships of these writing systems to pronunciation adds to the complexity of the study of visual perception and visual word recognition.
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