- Email: [email protected]
The nature of prolonged word search
BRAIN
AND
LANGUAGE
36,
411-419 (1989)
The Nature of Prolonged Word Search HAROLD GOODGLASS Boston VA Medical
Center and Aphasia Research Center, Department Boston University School of Medicine
of Neurology,
AND ARTHUR WINGFIELD AND SARAH Brandeis
C. WAYLAND
University, and Boston VA Medical Center and Aphasia Research Center, Department of Neurology, Boston University School of Medicine
Two alternative hypotheses were considered concerning the process of prolonged search for an uncommon word in response to hearing its definition. One alternative is that a conscious retrieval effort brings the target progressively closer to threshold. The second is that the retrieval process is a random neural exploration outside of conscious control. A tachistoscopic probe was devised to compare word recognition thresholds after 10 set versus 30 set of presumed search time. Results failed to show a difference between the two delay conditions and were interpreted as inconsistent with the first alternative but consistent with the second. D 19139 Academic
Press. Inc.
William James (1890) described in vivid prose the experience of searching for an elusive word and the way that parts of the desired word may be available even though the full word continues to remain inaccessible. Even when the desired word remains out of reach one nevertheless invariable knows with certainty whether an offered word fits the empty slot. In their classical “tip of the tongue” study, Brown and McNeil (1966) found that subjects often have considerable partial knowledge This work was supported in part by the Medical Research Service of the Veterans Administration and in part by PHS Grants NS 06209 and AC 04517 from the National Institutes of Health. The authors are grateful for the contributions of the other members of the Nemolinguistic Work Group in which this project was formulated: Jean Berko Gleason, Susan Kohn, Lise Menn, and Mary Hyde. The program for the Flash-probe computer presentation was designed by Diane Williams. We give special thanks to Idell Goldenberg, Lewis Shapiro, and Paula Nieman for valuable help in various stages of this project. 411 0093-934X/89 $3.00 Copyright 6 1989 by Academic Press. Inc. All rights of reproduction in any form reserved.
412
GOODGLASS,
WINGFIELD,
AND WAYLAND
about the phonological form of a target word which they still cannot fully retrieve. Although some of these effects may have been influenced by subjects’ general knowledge of English word structure (cf., Kohn et al., 1987; Koriat & Lieblich, 1974, 1975), the nature of the retrieval operations which may be performed in cases of difficult lexical access remain no less intriguing nearly 100 years after James’ initial observations. Numerous models of word finding have appeared in the literature, sometimes from a linear stage perspective (Goodglass, 1980; Lachman, 1973), and more recently, in terms of parallel interactive, or spreading activation, models (Ellis, 1985; Stemberger, 1985). It is also the case, however, that the process by which the phonological form of a desired word is ultimately brought above threshold for utterance has received little direct study and remains a question of basic interest in both normal and aphasic speech. It is nevertheless a common assumption that, in the course of extended effort to retrieve a word, we mobilize what fragmentary elements we are able to recover and the mnemonic associations that we have, so as to leave the smallest possible gap between that partial knowledge and the full target word we seek. This assumption implies that we carry out a purposeful search based on, or at least taking advantage of, our partial reconstruction of the desired word. Prior studies from this laboratory have yielded results which are most consistent with the view that delayed word retrieval entails a constrained random process which proceeds outside of voluntary control. Our investigation began with a completely informal introspective experiment in which we and several of our colleagues took turns in offering definitions of uncommon words which were likely to induce a tip-of-the-tongue (TOT) state in one or more of the group, during which time we were to call upon any associations that came to mind in an effort to bring the word to consciousness. In each instance of a delayed retrieval, the subjective experience was that the word suddenly materialized, without reference to the conscious associations. In daily life, while deliberately mobilized mnemonic devices often seem to be successful, at other times-perhaps most times-the elusive words seem to “pop” to mind, as in our informal experiment, rather than yielding to a systematic or effortful search. In our first formal experiment related to this topic, we examined the relationship between word frequency of a set of picture names and latencies to naming these pictures (Goodglass, Theurkauf & Wingfield, 1984). We found that for responses of up to 1500 msec latency, there was a strong (r = .77) correlation between name-word frequency and response latency, while beyond 1500 msec this correlation dropped below significance (r = .39). For latencies beyond 2500 msec, this relationship dropped away altogether. These results were seen as supporting the notion of a two-
PROLONGED
SEARCH
413
phase word retrieval process. The first, a rapid retrieval phase, conformed to the well-documented finding (Oldfield & Wingfield, 1965; Wingfield, 1967, 1968) of an inverse linear relationship between word frequency and latency. It seemed plausible that this phase terminated at 1500 msec and was succeeded by a protracted search phase in which retrieval time bore a nearly random relationship to word frequency. While plausible, this discontinuity of processes at 1500 msec is not the only possibility. For example, one could postulate a single mechanism in which the relationship between word frequency and response latency drops off continuously over time. That is, the intuitive appeal of an initial “automatic” stage, followed by an optional stage of controlled voluntary search, needed further examination. In a further study (Kohn et al., 1987), we assembled a set of tip-ofthe-tongue stimuli consisting of 102 definitions of uncommon words, equally distributed among lengths of one through five syllables. These definitions were given to 18 young adults with instructions to report aloud what they were thinking as they tried to retrieve each target word. If they failed to find the word after 2 min, the correct response was offered with an inquiry as to whether they had that target in mind, whether they only recognized it as correct, whether they had a different target in mind, or whether they were searching without a particular target word. The subjects’ interim responses were analyzed with respect to their relation (phonological, semantic, etc.) to the target and their ultimate success or level of knowledge, and also with respect to sequences of responses during any particular attempt. Two observations from this study appeared most consistent with the view that the subjects’ conscious interim associations had no influence on the retrieval process: the first was the absence of any progression toward the correct word in a sample of multiple attempts at a single target; the second was that there was no self-cuing effect as a result of matching the initial sound of the target in whole words offered as interim attempts. One observation that did support the possibility of self-cuing was that word fragments that matched the first sound of the target were more likely to precede a correct response than to precede an unconsummated TOT state. The best index of an ultimately successful response was the presence in one or more interim responses of phonological units of syllable or morpheme size that were shared by the target. The results were interpreted as most consistent with the view that the amount of partial phonological information with which the subject entered the word search determined the likelihood of success, but that the process of retrieving the word was inaccessible to conscious control. Translating these introspections into testable form, the issue is whether extended search for an uncommon word after being given its definition
414
GOODGLASS,
WINGFIELD,
AND WAYLAND
results in measurable changes in its accessibility, as compared to the state where less search time is allowed or when no definition at all has been presented. A positive finding would support the “search” hypothesis. The “pop” hypothesis is that, in most instances, the deliberate mobilization of associations produces an illusory impression of ferreting out the desired word, but that the process proceeds haphazardly and outside of voluntary control. More specifically, the “pop” theory suggests a neural model in which exploratory firing occurs randomly and that when, by chance, a pattern fires which brings fragments together beyond a critical level of activation, a rapid cascade ensues which brings the word to awareness in a subjectively instantaneous “pop.” According to this model, the word is no closer to threshold a second before the “pop” than at the beginning of the search. The process following the moment in which the critical level of activation is reached may be identical with the rapid phase of naming or production of an immediately available word. A relevant treatment of threshold notions within a parallel distributed processing (PDP) framework can be found in, for example, Stemberger (1985). In the following experiment, subjects were read the definitions of our TOT test. Assuming that the words are in the subjects’ vocabulary, a feature that must be interrogated in any such experiment, a search hypothesis would assume that subjects allowed 30 set, would, on average, “get farther” in their search than a subject allowed only 10 sec. To test this relative accessibility, subjects were given a sequence of tachistoscopically presented words with exposure durations increased until they were correctly recognized. Unlike traditional threshold studies in which subjects are given time to respond after each presentation before being given the next longer one, in this case the presentation series were rapid and automatic to minimize the total elapsed time from initial exposure to suprathreshold presentation. This was done to reduce the likelihood that subjects might coincidentally produce the words with the passage of time without reference to the tachistoscopic presentations. The recognition times for the words presented with lo- and with 30-set delays were then compared with a base-line control condition consisting of words presented without prior definitions. This rapid presentation technique, which we refer to as Flash-probe, was intended to give an index of the word’s threshold at the moment of testing. If the results show 10 and 30 set of putative search time to have different effects on recognition times for the desired target words, the “search” hypothesis will be supported. However, negative results would only be a weak indicator of the contrary “pop” hypothesis which holds that the neural counterpart of extended voluntary word search is actually a random effort. To regard it as direct support would involve assuming that the null hypothesis had been proven.
PROLONGED SEARCH
415
METHODS Definitions and targets. The stimuli consisted of 93 definitions and their target words taken from Kohn et al. (1987). The definitions were in the style of dictionary entries, ranging from just a few words in length (e.g., “female hog” for sow), to definitions 11 or 12 words in length (e.g., “transformation from one form to another, as from a caterpiller to a butterfly” for metamorphosis). The 93 target words consisted of 20 one-syllable, 20 two-syllable, 20 three-syllable, 20 four-syllable, and 13 five-syllable words. Procedures. In the two definition/delay conditions, each definition was read aloud to the subject. As the subject heard the definition, he or she was to try to produce the target word aloud as quickly as possible. If the target word was correctly named before the visual presentations were begun, that trial was ended and the next definition was read. If the subject did not produce the correct word after either 10 or 30 set had elapsed after hearing the definition (depending on the condition), the subject received a verbal “ready” warning. This warning was followed immediately by a series of rapid visual presentations of the correct target word on the display screen of an Apple IIe microcomputer. The subject’s task was to observe the sequence of visual presentations and to stop the sequence by saying aloud the stimulus word the instant it could be recognized. Target words were presented in uppercase letters beginning at 16.7 msec and followed automatically at SOO-msecintervals by successive presentations of the target word with each successive presentation increasing in 16.7-msec increments. The SOO-msecintervals between successive presentations were filled by a visual mask composed of a random dot matrix which appeared in the same spatial position as occupied by the longest of the target words. The first presentation of 16.7 msec was also preceded by the 500-msec visual mask. The series of mask-stimulus-mask presentations continued automatically until the subject gave the correct response. At that point the presentation sequence was interrupted and the exposure duration at which the word was correctly identified was recorded. Using increments of 16.7 msec in each cycle and a constant 500-msec masked IS1 allowed the sampling of the first seven exposure levels (i.e., exposure durations up to 117 msec) in under 4 sec. The unit of 16.7 msec was constrained by the “refresh cycle” of the Apple computer. To test the sensitivity of this presentation technique in showing effects of priming by a prior context, we conducted a pilot study in which 20 subjects were shown 46 words using this rapid sequence presentation technique. In a counterbalanced design, half of the words that each subject saw were preceeded immediately by a spoken superordinate cue that limited the range of alternative responses. Two examples were “A musical symbol” preceeding the word CLEF, and “A type of oration” preceeding the word VALEDICTORY. The remaining half were presented alone without such cues. The cued words were recognized with an average presentation duration of 133 msec, while the same words not preceded by a superordinate cue required a mean of 147 msec for correct recognition, r(45) = 5.89, p < ,001. We were thus satisfied that the technique itself was a sensitive enough one for our purposes. The present experiment was designed to allow each subject potentially to receive all 93 targets for recognition threshold measurement; 31 words in the No Definition Control condition, 31 words with a IO-set delay interval between the end of the spoken definition and the onset of the presentation sequence, and 31 words with a 30-set delay between the end of the definition and the onset of the presentations. In fact, however, the number of words which reached the lo- and 30-set delay conditions varied unpredictably from subject to subject, depending on how many of these words were not produced before the rapid presentation sequences began. In the two definition/delay conditions, after each word was correctly identified, subjects were asked whether the word was in their active vocabulary, and whether they recognized that it was the correct response for the presented definition, even though they had been
416
GOODGLASS, WINGFIELD,
AND WAYLAND
unable to think of it within the time limit allowed. These responses were categorized as TOT responses, and only these responses were considered in our analysis. In some cases after seeing the full target word subjects claimed that the word was not in their active vocabulary or that they would not have thought of this word in the context of the presented definition. These were categorized as NFD (Not From Definition) and were excluded from subsequent analyses. The presentations were blocked by condition, and the order of presentation of conditions was counterbalanced across subjects such that, by the end of the experiment, each condition was given in each serial order an equal number of times. Subjects. A total of 54 subjects were tested. All were university undergraduates or graduate staff assistants who were naive as to the purposes of the experiment.
RESULTS Data Available No definition control. Of the 1674 possible thresholds (31 word’s per subject x 54 subjects), a total of 66 responses (4%) were lost due to apparatus failure or experimenter error (e.g., inadvertently terminating the exposure series to an incorrect response). ZO-set delay. Of the 1674 possible thresholds in this condition, a total of 740 target words (44% of the total presentations for this condition) were given by the subjects before the computer presentations could begin, and a further 85 words (5%) were lost due to apparatus failure or experimenter error. Of the remaining 849 responses, 162 (10% of the total possible responses for this condition) were TOT responses, and 687 (41% of the total possible responses for this condition) were NFD responses. 30-set delay. Of the 1674 possible responses, 802 target words (48% of the total responses for this condition) were given by the subject before the computer presentations could begin. A further 78 responses (5%) were lost due to apparatus failure or experimenter error. Of the remaining 794 responses, 91 responses (5% of the total possible responses for this condition) were TOT responses, and 703 responses (42% of the total possible responses for this condition) were NFD responses. Measured Thresholds In this paradigm, one could anticipate wide variability in how often any particular word would be likely to appear in a TOT condition. For example, while the mean for the No Definition control condition would have all 93 words represented, the TOT condition might, on average, have only the easier words (i.e., the NFD cases will have been pulled out). Thus, apparently shorter recognition thresholds under the TOT conditions than for the No Definition Control could simply be an artifact of this effect. Similarly, in all cases, the easier the word, the more likely it would be to have been given from its definition alone prior to the onset of the tachistoscopic presentations, and this in turn would, on average, be more likely for the 30- than for the IO-set delay conditions.
417
PROLONGED SEARCH
160
1
no definition control
ten second delay
thirty
second delay
Target Word Presentation Conditions FIG. 1. Mean Flash-probe recognition thresholds for target words presented without prior definitions (No Definition Control) and when preceeded by definitions either 10 or 30 set prior to Flash-probe presentation sequence. Vertical bars represent standard errors of the means.
For these reasons, Fig. 1 shows mean thresholds only for those 43 words that occurred in all three conditions (No Definition, lo- and 30set TOTS). (These means are necessarily based on different numbers of data points for this same subset of 43 words in the three conditions. That is, the mean threshold for the No Definition Control condition was based on a total of 795 thresholds, the mean for the IO-set delay condition was based on 116 thresholds, and the mean for the 30-set delay was based on a total of only 77 thresholds. This systematic reduction in numbers is a consequence of fewer words surviving to 30 set than to just 10 sec. These differences in numbers going into the three means accounts for differences in standard errors of the means plotted for the three conditions in Fig. 1.) As implied by Fig. 1, there was an overall significant effect of conditions F(2, 985) = 46.93, p < .OOl. Scheffe post hoc tests showed that the difference between thresholds for the lo-set vs. 30-set delay conditions was not significant, but that both were significantly different from the
418
GOODGLASS,
WINGFIELD,
AND WAYLAND
thresholds for the No Definition Control condition (r, < .OOl in both cases). DISCUSSION
The results of this experiment showed that the same set of words without a prior definition required longer presentation times for correct recognition than those presented with definitions. This result generally replicated the findings of our pilot study. Indeed, in the No Definition Control condition in the present experiment, the mean recognition threshold was 145 msec as compared with the control condition threshold of 147 msec in the pilot study. In this case, however, the availability of the full definitions of the target words reduced the thresholds by between 38 and 39 msec (for the 30- and IO-set delay conditions, respectively), relative to the control condition, rather than the 14-msec reduction in the pilot study which used less constraining superordinate cues. In the Kohn et al. (1987) experiment previously described, all of the target words were semantically specified at the outset by their presented definitions, and our focus on subjects’ phonological knowledge was as inferred from their interim response attempts. In the present experiment, the independent variable was whether the subject entered the recognition task with no semantic specification versus full semantic specification as provided by the definition. The significant reduction in recognition thresholds with this specification can be attributed to a constraint on the number or range of possible responses. Our primary focus, however, rests on the finding that increasing the delay between presentation of the definition and the onset of the target word presentation sequence from 10 to 30 set did not further reduce the recognition thresholds as would have been predicted by a progressive search hypothesis. We should note two cautions associated with this experiment. The first is that this experiment had to involve a technique in which only a subset of responses-those representing a TOT condition-could be used for our analysis. The second is that while a significant difference between IO- and 30-set delays would have favored a “search” hypothesis, a finding of no difference, an acceptance of the null hypothesis, as it were, can at best only fail to support a progressive search. It cannot, in itself, more directly favor a “pop” hypothesis. Although the proposed model of word search is highly speculative, we have obtained a succession of experimental results which make it plausible by exclusion, since the alternative of a progressive search is not supported by data. We do not believe, however, that the establishment of the pop hypothesis is an intractable task. It may be approached through any on-line technique which is sensitive to brain activity in the short period of time between attainment of the critical threshold and the response. For example, if the word-search period is characterized by a steady state
PROLONGED SEARCH
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of brain activity which changes abruptly in the several hundred milliseconds preceding successful retrieval, we would have direct support for the pop hypothesis. This approach may be within the reach of current technology and would seem to be the next step to take. REFERENCES Brown, R., & McNeill, D. 1966. the “tip of the tongue” phenomenon. Journal of Verbal Learning
and Verbal Behavior,
5, 325-337.
Ellis, A. W. 1985. The production of spoken words: A cognitive neuropsychological perspective. In A. W. Ellis (Ed.), Progress in the psychology oflanguage. Hillsdale, NJ: Erlbaum. Vol. 2, pp. 107-145. Goodglass, H. 1980. Disorders of naming following brain injury. American Scientisf, 68, 647-655. Goodglass, H., Theurkauf, J. C., & Wingfield, A. (1984). Naming latencies as evidence for two modes of lexical retrieval. Applied Psycholinguistics, 5, 135-146. James, W. 1890. The priniciples of psychology. New York: Holt. Vol. I. Kohn, S. E., Wingfield, A., Menn, L., Goodglass, H., Gleason, J. B., & Hyde, M. 1987. Lexical retrieval: The tip of the tongue phenomenon. Applied Psycholinguistics, 8, 245-266. Koriat, A., & Lieblich, I. 1974. What does a person in a “TOT” state know that a person in a “don’t know” state doesn’t know? Memory and Cognition, 2, 647-655. Koriat, A., & Lieblich, I. 1975. Examination of the letter serial position effect in the “TOT” and the “don’t know” state. Bulletin of the Psychonomic Society, 6, 539541. Lachman, R. 1973. Uncertainty effects on time to access the internal lexicon. Journal of Experimental Psychology, 99, 199-208. Oldfield, R. C., & Wingfield, A. 1965. Response latencies in naming objects. Quarterly Journal
of Experimental
Psychology,
17, 273-281.
Stemberger, J. P. 1985. An interactive model of language production. In A. W. Ellis (Ed.), Progress in the psychology of language. Hillsdale, NJ: Erlbaum. Vol. 1, pp. 143-186. Wingfield, A. 1967. Perceptual and response hierarchies in object identification. Acta Psychologica,
26, 216-226.
Wingfield, A. 1968. Effects of frequency on identification and naming of objects. American Journal of Psychology, 81, 226-234.
AND
LANGUAGE
36,
411-419 (1989)
The Nature of Prolonged Word Search HAROLD GOODGLASS Boston VA Medical
Center and Aphasia Research Center, Department Boston University School of Medicine
of Neurology,
AND ARTHUR WINGFIELD AND SARAH Brandeis
C. WAYLAND
University, and Boston VA Medical Center and Aphasia Research Center, Department of Neurology, Boston University School of Medicine
Two alternative hypotheses were considered concerning the process of prolonged search for an uncommon word in response to hearing its definition. One alternative is that a conscious retrieval effort brings the target progressively closer to threshold. The second is that the retrieval process is a random neural exploration outside of conscious control. A tachistoscopic probe was devised to compare word recognition thresholds after 10 set versus 30 set of presumed search time. Results failed to show a difference between the two delay conditions and were interpreted as inconsistent with the first alternative but consistent with the second. D 19139 Academic
Press. Inc.
William James (1890) described in vivid prose the experience of searching for an elusive word and the way that parts of the desired word may be available even though the full word continues to remain inaccessible. Even when the desired word remains out of reach one nevertheless invariable knows with certainty whether an offered word fits the empty slot. In their classical “tip of the tongue” study, Brown and McNeil (1966) found that subjects often have considerable partial knowledge This work was supported in part by the Medical Research Service of the Veterans Administration and in part by PHS Grants NS 06209 and AC 04517 from the National Institutes of Health. The authors are grateful for the contributions of the other members of the Nemolinguistic Work Group in which this project was formulated: Jean Berko Gleason, Susan Kohn, Lise Menn, and Mary Hyde. The program for the Flash-probe computer presentation was designed by Diane Williams. We give special thanks to Idell Goldenberg, Lewis Shapiro, and Paula Nieman for valuable help in various stages of this project. 411 0093-934X/89 $3.00 Copyright 6 1989 by Academic Press. Inc. All rights of reproduction in any form reserved.
412
GOODGLASS,
WINGFIELD,
AND WAYLAND
about the phonological form of a target word which they still cannot fully retrieve. Although some of these effects may have been influenced by subjects’ general knowledge of English word structure (cf., Kohn et al., 1987; Koriat & Lieblich, 1974, 1975), the nature of the retrieval operations which may be performed in cases of difficult lexical access remain no less intriguing nearly 100 years after James’ initial observations. Numerous models of word finding have appeared in the literature, sometimes from a linear stage perspective (Goodglass, 1980; Lachman, 1973), and more recently, in terms of parallel interactive, or spreading activation, models (Ellis, 1985; Stemberger, 1985). It is also the case, however, that the process by which the phonological form of a desired word is ultimately brought above threshold for utterance has received little direct study and remains a question of basic interest in both normal and aphasic speech. It is nevertheless a common assumption that, in the course of extended effort to retrieve a word, we mobilize what fragmentary elements we are able to recover and the mnemonic associations that we have, so as to leave the smallest possible gap between that partial knowledge and the full target word we seek. This assumption implies that we carry out a purposeful search based on, or at least taking advantage of, our partial reconstruction of the desired word. Prior studies from this laboratory have yielded results which are most consistent with the view that delayed word retrieval entails a constrained random process which proceeds outside of voluntary control. Our investigation began with a completely informal introspective experiment in which we and several of our colleagues took turns in offering definitions of uncommon words which were likely to induce a tip-of-the-tongue (TOT) state in one or more of the group, during which time we were to call upon any associations that came to mind in an effort to bring the word to consciousness. In each instance of a delayed retrieval, the subjective experience was that the word suddenly materialized, without reference to the conscious associations. In daily life, while deliberately mobilized mnemonic devices often seem to be successful, at other times-perhaps most times-the elusive words seem to “pop” to mind, as in our informal experiment, rather than yielding to a systematic or effortful search. In our first formal experiment related to this topic, we examined the relationship between word frequency of a set of picture names and latencies to naming these pictures (Goodglass, Theurkauf & Wingfield, 1984). We found that for responses of up to 1500 msec latency, there was a strong (r = .77) correlation between name-word frequency and response latency, while beyond 1500 msec this correlation dropped below significance (r = .39). For latencies beyond 2500 msec, this relationship dropped away altogether. These results were seen as supporting the notion of a two-
PROLONGED
SEARCH
413
phase word retrieval process. The first, a rapid retrieval phase, conformed to the well-documented finding (Oldfield & Wingfield, 1965; Wingfield, 1967, 1968) of an inverse linear relationship between word frequency and latency. It seemed plausible that this phase terminated at 1500 msec and was succeeded by a protracted search phase in which retrieval time bore a nearly random relationship to word frequency. While plausible, this discontinuity of processes at 1500 msec is not the only possibility. For example, one could postulate a single mechanism in which the relationship between word frequency and response latency drops off continuously over time. That is, the intuitive appeal of an initial “automatic” stage, followed by an optional stage of controlled voluntary search, needed further examination. In a further study (Kohn et al., 1987), we assembled a set of tip-ofthe-tongue stimuli consisting of 102 definitions of uncommon words, equally distributed among lengths of one through five syllables. These definitions were given to 18 young adults with instructions to report aloud what they were thinking as they tried to retrieve each target word. If they failed to find the word after 2 min, the correct response was offered with an inquiry as to whether they had that target in mind, whether they only recognized it as correct, whether they had a different target in mind, or whether they were searching without a particular target word. The subjects’ interim responses were analyzed with respect to their relation (phonological, semantic, etc.) to the target and their ultimate success or level of knowledge, and also with respect to sequences of responses during any particular attempt. Two observations from this study appeared most consistent with the view that the subjects’ conscious interim associations had no influence on the retrieval process: the first was the absence of any progression toward the correct word in a sample of multiple attempts at a single target; the second was that there was no self-cuing effect as a result of matching the initial sound of the target in whole words offered as interim attempts. One observation that did support the possibility of self-cuing was that word fragments that matched the first sound of the target were more likely to precede a correct response than to precede an unconsummated TOT state. The best index of an ultimately successful response was the presence in one or more interim responses of phonological units of syllable or morpheme size that were shared by the target. The results were interpreted as most consistent with the view that the amount of partial phonological information with which the subject entered the word search determined the likelihood of success, but that the process of retrieving the word was inaccessible to conscious control. Translating these introspections into testable form, the issue is whether extended search for an uncommon word after being given its definition
414
GOODGLASS,
WINGFIELD,
AND WAYLAND
results in measurable changes in its accessibility, as compared to the state where less search time is allowed or when no definition at all has been presented. A positive finding would support the “search” hypothesis. The “pop” hypothesis is that, in most instances, the deliberate mobilization of associations produces an illusory impression of ferreting out the desired word, but that the process proceeds haphazardly and outside of voluntary control. More specifically, the “pop” theory suggests a neural model in which exploratory firing occurs randomly and that when, by chance, a pattern fires which brings fragments together beyond a critical level of activation, a rapid cascade ensues which brings the word to awareness in a subjectively instantaneous “pop.” According to this model, the word is no closer to threshold a second before the “pop” than at the beginning of the search. The process following the moment in which the critical level of activation is reached may be identical with the rapid phase of naming or production of an immediately available word. A relevant treatment of threshold notions within a parallel distributed processing (PDP) framework can be found in, for example, Stemberger (1985). In the following experiment, subjects were read the definitions of our TOT test. Assuming that the words are in the subjects’ vocabulary, a feature that must be interrogated in any such experiment, a search hypothesis would assume that subjects allowed 30 set, would, on average, “get farther” in their search than a subject allowed only 10 sec. To test this relative accessibility, subjects were given a sequence of tachistoscopically presented words with exposure durations increased until they were correctly recognized. Unlike traditional threshold studies in which subjects are given time to respond after each presentation before being given the next longer one, in this case the presentation series were rapid and automatic to minimize the total elapsed time from initial exposure to suprathreshold presentation. This was done to reduce the likelihood that subjects might coincidentally produce the words with the passage of time without reference to the tachistoscopic presentations. The recognition times for the words presented with lo- and with 30-set delays were then compared with a base-line control condition consisting of words presented without prior definitions. This rapid presentation technique, which we refer to as Flash-probe, was intended to give an index of the word’s threshold at the moment of testing. If the results show 10 and 30 set of putative search time to have different effects on recognition times for the desired target words, the “search” hypothesis will be supported. However, negative results would only be a weak indicator of the contrary “pop” hypothesis which holds that the neural counterpart of extended voluntary word search is actually a random effort. To regard it as direct support would involve assuming that the null hypothesis had been proven.
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415
METHODS Definitions and targets. The stimuli consisted of 93 definitions and their target words taken from Kohn et al. (1987). The definitions were in the style of dictionary entries, ranging from just a few words in length (e.g., “female hog” for sow), to definitions 11 or 12 words in length (e.g., “transformation from one form to another, as from a caterpiller to a butterfly” for metamorphosis). The 93 target words consisted of 20 one-syllable, 20 two-syllable, 20 three-syllable, 20 four-syllable, and 13 five-syllable words. Procedures. In the two definition/delay conditions, each definition was read aloud to the subject. As the subject heard the definition, he or she was to try to produce the target word aloud as quickly as possible. If the target word was correctly named before the visual presentations were begun, that trial was ended and the next definition was read. If the subject did not produce the correct word after either 10 or 30 set had elapsed after hearing the definition (depending on the condition), the subject received a verbal “ready” warning. This warning was followed immediately by a series of rapid visual presentations of the correct target word on the display screen of an Apple IIe microcomputer. The subject’s task was to observe the sequence of visual presentations and to stop the sequence by saying aloud the stimulus word the instant it could be recognized. Target words were presented in uppercase letters beginning at 16.7 msec and followed automatically at SOO-msecintervals by successive presentations of the target word with each successive presentation increasing in 16.7-msec increments. The SOO-msecintervals between successive presentations were filled by a visual mask composed of a random dot matrix which appeared in the same spatial position as occupied by the longest of the target words. The first presentation of 16.7 msec was also preceded by the 500-msec visual mask. The series of mask-stimulus-mask presentations continued automatically until the subject gave the correct response. At that point the presentation sequence was interrupted and the exposure duration at which the word was correctly identified was recorded. Using increments of 16.7 msec in each cycle and a constant 500-msec masked IS1 allowed the sampling of the first seven exposure levels (i.e., exposure durations up to 117 msec) in under 4 sec. The unit of 16.7 msec was constrained by the “refresh cycle” of the Apple computer. To test the sensitivity of this presentation technique in showing effects of priming by a prior context, we conducted a pilot study in which 20 subjects were shown 46 words using this rapid sequence presentation technique. In a counterbalanced design, half of the words that each subject saw were preceeded immediately by a spoken superordinate cue that limited the range of alternative responses. Two examples were “A musical symbol” preceeding the word CLEF, and “A type of oration” preceeding the word VALEDICTORY. The remaining half were presented alone without such cues. The cued words were recognized with an average presentation duration of 133 msec, while the same words not preceded by a superordinate cue required a mean of 147 msec for correct recognition, r(45) = 5.89, p < ,001. We were thus satisfied that the technique itself was a sensitive enough one for our purposes. The present experiment was designed to allow each subject potentially to receive all 93 targets for recognition threshold measurement; 31 words in the No Definition Control condition, 31 words with a IO-set delay interval between the end of the spoken definition and the onset of the presentation sequence, and 31 words with a 30-set delay between the end of the definition and the onset of the presentations. In fact, however, the number of words which reached the lo- and 30-set delay conditions varied unpredictably from subject to subject, depending on how many of these words were not produced before the rapid presentation sequences began. In the two definition/delay conditions, after each word was correctly identified, subjects were asked whether the word was in their active vocabulary, and whether they recognized that it was the correct response for the presented definition, even though they had been
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unable to think of it within the time limit allowed. These responses were categorized as TOT responses, and only these responses were considered in our analysis. In some cases after seeing the full target word subjects claimed that the word was not in their active vocabulary or that they would not have thought of this word in the context of the presented definition. These were categorized as NFD (Not From Definition) and were excluded from subsequent analyses. The presentations were blocked by condition, and the order of presentation of conditions was counterbalanced across subjects such that, by the end of the experiment, each condition was given in each serial order an equal number of times. Subjects. A total of 54 subjects were tested. All were university undergraduates or graduate staff assistants who were naive as to the purposes of the experiment.
RESULTS Data Available No definition control. Of the 1674 possible thresholds (31 word’s per subject x 54 subjects), a total of 66 responses (4%) were lost due to apparatus failure or experimenter error (e.g., inadvertently terminating the exposure series to an incorrect response). ZO-set delay. Of the 1674 possible thresholds in this condition, a total of 740 target words (44% of the total presentations for this condition) were given by the subjects before the computer presentations could begin, and a further 85 words (5%) were lost due to apparatus failure or experimenter error. Of the remaining 849 responses, 162 (10% of the total possible responses for this condition) were TOT responses, and 687 (41% of the total possible responses for this condition) were NFD responses. 30-set delay. Of the 1674 possible responses, 802 target words (48% of the total responses for this condition) were given by the subject before the computer presentations could begin. A further 78 responses (5%) were lost due to apparatus failure or experimenter error. Of the remaining 794 responses, 91 responses (5% of the total possible responses for this condition) were TOT responses, and 703 responses (42% of the total possible responses for this condition) were NFD responses. Measured Thresholds In this paradigm, one could anticipate wide variability in how often any particular word would be likely to appear in a TOT condition. For example, while the mean for the No Definition control condition would have all 93 words represented, the TOT condition might, on average, have only the easier words (i.e., the NFD cases will have been pulled out). Thus, apparently shorter recognition thresholds under the TOT conditions than for the No Definition Control could simply be an artifact of this effect. Similarly, in all cases, the easier the word, the more likely it would be to have been given from its definition alone prior to the onset of the tachistoscopic presentations, and this in turn would, on average, be more likely for the 30- than for the IO-set delay conditions.
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1
no definition control
ten second delay
thirty
second delay
Target Word Presentation Conditions FIG. 1. Mean Flash-probe recognition thresholds for target words presented without prior definitions (No Definition Control) and when preceeded by definitions either 10 or 30 set prior to Flash-probe presentation sequence. Vertical bars represent standard errors of the means.
For these reasons, Fig. 1 shows mean thresholds only for those 43 words that occurred in all three conditions (No Definition, lo- and 30set TOTS). (These means are necessarily based on different numbers of data points for this same subset of 43 words in the three conditions. That is, the mean threshold for the No Definition Control condition was based on a total of 795 thresholds, the mean for the IO-set delay condition was based on 116 thresholds, and the mean for the 30-set delay was based on a total of only 77 thresholds. This systematic reduction in numbers is a consequence of fewer words surviving to 30 set than to just 10 sec. These differences in numbers going into the three means accounts for differences in standard errors of the means plotted for the three conditions in Fig. 1.) As implied by Fig. 1, there was an overall significant effect of conditions F(2, 985) = 46.93, p < .OOl. Scheffe post hoc tests showed that the difference between thresholds for the lo-set vs. 30-set delay conditions was not significant, but that both were significantly different from the
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thresholds for the No Definition Control condition (r, < .OOl in both cases). DISCUSSION
The results of this experiment showed that the same set of words without a prior definition required longer presentation times for correct recognition than those presented with definitions. This result generally replicated the findings of our pilot study. Indeed, in the No Definition Control condition in the present experiment, the mean recognition threshold was 145 msec as compared with the control condition threshold of 147 msec in the pilot study. In this case, however, the availability of the full definitions of the target words reduced the thresholds by between 38 and 39 msec (for the 30- and IO-set delay conditions, respectively), relative to the control condition, rather than the 14-msec reduction in the pilot study which used less constraining superordinate cues. In the Kohn et al. (1987) experiment previously described, all of the target words were semantically specified at the outset by their presented definitions, and our focus on subjects’ phonological knowledge was as inferred from their interim response attempts. In the present experiment, the independent variable was whether the subject entered the recognition task with no semantic specification versus full semantic specification as provided by the definition. The significant reduction in recognition thresholds with this specification can be attributed to a constraint on the number or range of possible responses. Our primary focus, however, rests on the finding that increasing the delay between presentation of the definition and the onset of the target word presentation sequence from 10 to 30 set did not further reduce the recognition thresholds as would have been predicted by a progressive search hypothesis. We should note two cautions associated with this experiment. The first is that this experiment had to involve a technique in which only a subset of responses-those representing a TOT condition-could be used for our analysis. The second is that while a significant difference between IO- and 30-set delays would have favored a “search” hypothesis, a finding of no difference, an acceptance of the null hypothesis, as it were, can at best only fail to support a progressive search. It cannot, in itself, more directly favor a “pop” hypothesis. Although the proposed model of word search is highly speculative, we have obtained a succession of experimental results which make it plausible by exclusion, since the alternative of a progressive search is not supported by data. We do not believe, however, that the establishment of the pop hypothesis is an intractable task. It may be approached through any on-line technique which is sensitive to brain activity in the short period of time between attainment of the critical threshold and the response. For example, if the word-search period is characterized by a steady state
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of brain activity which changes abruptly in the several hundred milliseconds preceding successful retrieval, we would have direct support for the pop hypothesis. This approach may be within the reach of current technology and would seem to be the next step to take. REFERENCES Brown, R., & McNeill, D. 1966. the “tip of the tongue” phenomenon. Journal of Verbal Learning
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Ellis, A. W. 1985. The production of spoken words: A cognitive neuropsychological perspective. In A. W. Ellis (Ed.), Progress in the psychology oflanguage. Hillsdale, NJ: Erlbaum. Vol. 2, pp. 107-145. Goodglass, H. 1980. Disorders of naming following brain injury. American Scientisf, 68, 647-655. Goodglass, H., Theurkauf, J. C., & Wingfield, A. (1984). Naming latencies as evidence for two modes of lexical retrieval. Applied Psycholinguistics, 5, 135-146. James, W. 1890. The priniciples of psychology. New York: Holt. Vol. I. Kohn, S. E., Wingfield, A., Menn, L., Goodglass, H., Gleason, J. B., & Hyde, M. 1987. Lexical retrieval: The tip of the tongue phenomenon. Applied Psycholinguistics, 8, 245-266. Koriat, A., & Lieblich, I. 1974. What does a person in a “TOT” state know that a person in a “don’t know” state doesn’t know? Memory and Cognition, 2, 647-655. Koriat, A., & Lieblich, I. 1975. Examination of the letter serial position effect in the “TOT” and the “don’t know” state. Bulletin of the Psychonomic Society, 6, 539541. Lachman, R. 1973. Uncertainty effects on time to access the internal lexicon. Journal of Experimental Psychology, 99, 199-208. Oldfield, R. C., & Wingfield, A. 1965. Response latencies in naming objects. Quarterly Journal
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Stemberger, J. P. 1985. An interactive model of language production. In A. W. Ellis (Ed.), Progress in the psychology of language. Hillsdale, NJ: Erlbaum. Vol. 1, pp. 143-186. Wingfield, A. 1967. Perceptual and response hierarchies in object identification. Acta Psychologica,
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