- Email: [email protected]
Memory determinants of response latency to produce speech
Acta Psychologica 50 ( 1982) 127- 142 North-Holland Publishing Company
MEMORY DETERMINANTS SPEECH * Susan F. EHRLICH
and William
127
OF RESPONSE
LATENCY
TO PRODUCE
E. COOPER
I~arocrrdU~~roers~!,: USA Accepted
May 1981
In three experiments, subjects were asked to memorize related phrase pairs and then to produce one of these phrases from a cue. In Experiment 1, it was found that both memorization times and response latencies increased with the number of words that differed between the phrases. In Experiment 2 and 3. it was shown that the presence of a strong modifying or semantic relationship between words in one phrase influenced both memorization time and response latency when those same words were contrasted between the two phrases. The implications of the results for models of storage, retrieval, and planning of speech are considered.
In this paper a new approach for studying response latency to produce speech is described. Subjects were presented with two noun phrases to memorize. The phrases were associated to prompts during the memorization interval, and subjects were instructed to produce one of the phrases after receiving a prompt. The use of only two potential responses has generally been avoided in response latency experiments because of the possibility that subjects may anticipate one of the responses, thus influencing the type of processing occurring in the response latency interval and adding to latency variability has yielded (Klapp 1979). We have found, however, that this procedure significant effects, overriding response variability, that allow us to gain information about speech planning operations that are dependent on the relationship between the two potential responses. In the first experiment, both potential responses contained a head noun and two prepositional phrases. The number of nouns that were shared between the phrases was varied between 0 and 3. The amount of time required to memorize the phrases was recorded as well as the response latency to initiate production of one of the phrases from the prompt. Pilot data had suggested that subjects * This work was supported by NIH Grant NS-15059. We thank Scott Bradner and the Computer Based Laboratory at Harvard for facilities and programming. In addition, we thank Trude Huber for help in running SUbJects and providing suggestions. Mailing address: SF. Ehrlich. 1202 William James Hall, Dept. of Psychology and Social Relations, Harvard University, 33 Kirkland Street, Cambridge, MA 02138. USA. 0001-69 18/82/0000~0000/$02.75
0 1982 North-Holland
were
able to take advantage
memorization interval experiment was a first
of the commonality
of the phrases
both
during
the
and during the response latency interval, and this attempt to examine the advantage of the commonality
formally.
Experiment
1
Method SubJects
Nine members of the Harvard University community, one male and eight females, participated as paid volunteers in the experiment. Three other Ss were eliminated because of their inability to consistently trigger the reaction time equipment used in the experiment, and two other Ss were eliminated before any statistical analyses were carried out because of their unusually long response latencies. Muterids Six phrase groups were developed. Each phrase consisted of a head noun and two prepositional phrases. For each phrase group there were two base phrases, and the eight experimental conditions (having identical stress patterns) were derived from these base phrases. Each phrase started with the word “A” because the vowel was found to be a more consistent trigger for the voice key than another candidate word, “The”, which begins with a low amplitude fricative. The base phrases are listed in table 1. During an experimental trial, the S was asked to memorize two of the phrases derived from the base phrases. The two phrases were either (I) identical, (2) differing in terms of one noun, (3) differing in terms of two nouns or (4) differing in terms of all
Table I Base phrases
used to generate
phrase
pairs in experiment
1
Set I
A photo of a bush in the garden (bedroom) A drawing of a tree in the valley (hallway)
Set 2
A girl in a van with a bike rack (mailman) A man in a car with a sunroof (robber)
set 3
A casino with a gift shop in the lobby (country) A museum with a snack bar in the basement (city)
Set 4
A truck with olives in barrels (Texas) A store with pickles in bottles (Utah)
Set 5
A lawyer in the mansion with a swimming pool (leisure suit) A doctor in the clubhouse with a sauna bath (polo shirt)
Set 6
A novel about mountains in Poland (Hilles) A pamphlet about rivers in England (Widener)
three nouns. The locations of the contrasting words were varied systematically, resulting in eight permutations. A second independent variable was superimposed on these eight types of pairs. The last prepositional phrase in the noun phrase either modified the head noun (MH) or the noun in the preceding prepositional phrase (MPP), resulting in 16 different conditions for each of the six base pairs. The phrases with the MH structure were identical to the phrases with the MPP structure except for the last noun. The nouns used for the MH structures are presented in parentheses in table 1. It should be noted here that while an effort was made to make the two different modifying structures as distinct as possible, the phrases were still potentially ambiguous, particularly if the Ss elected to encode absurd interpretations such as “(A man in a car) with a sunroof”. Equipment
The Ss were seated in front of a cathode ray tube that was controlled by a PDP-4 Computer. New trials were triggered by the S with a button. Ss wore headphones and spoke into a microphone which fed into a Grason-Stadler voice key (Model no. E7300-Al). The appropriateness of the onset delay setting and the gain setting for the voice key was examined visually using the AUDITS computer program (Huggins 1969). With this program, it was possible to measure the time delay between the onset of the precue beep and the onset of the waveform of the S’s voice, displayed on a CRT. Procedure
Each S participated individually in one session with an average duration of 90 min. When the S entered the experimental room, he was seated in front of the cathode ray tube, and the procedure was described. The experiment consisted of a series of 96 trials. Each of the 96 trials was randomly assigned to one of three blocks, and the order of the trials within the blocks was randomized. The location of a particular phrase in the top or bottom of the display was randomized, and the use of a Top vs. Bottom cue for particular trials was chosen at random. All Ss saw the same three trial blocks, but the order of the blocks was rotated for the nine Ss. The test trials were preceded by a practice block of 24 trials. Ss were given breaks after each trial block. On each trial, two phrases appeared on the screen, one on the top with a “T” printed in front if it and one on the bottom with a “B” in front of it. Ss were told to take as much as they needed to memorize the phrases and to signal their completion of the memorization phase by pressing a button. At that point, the phrases disappeared from the screen, followed by a one second period. A precue beep was then presented over the headphones. A second later, a cue appeared on the screen. The cue was either a “T” or a “B”, and the letter was positioned in the same location as the original “T” or “B” had been when the phrases still appeared on the screen. The Ss were instructed to produce the phrase that corresponded to the letter as quickly as possible into the microphone. This general instruction was given only once in an attempt to induce differential response latencies. However, no special premium was placed on either speed of production or speed of response initiation during the experimental session. Ss’ utterances appeared to fall within a normal range of speaking rates. The S then pushed a button to start the next trial. The amount of time the S spent looking at each phrase pair (memorization time) and the period between the onset of the cue and the onset of the S’s voice (response latency) were recorded by the computer.
Ss were instructed to speak clearly, to avoid extraneous activity during the memorization period, and to avoid errors. Cash bonuses were given for accuracy. Ss were also cautioned not to use any unusual mnemonic strategies to help them remember the phrases. During the experimental session, the experimenter monitored the Ss’ responses and wrote down any errors. At the same time, the experimenter watched the screen to observe when the “T” or “B” cue disappeared. The computer had been programmed to terminate display of the cue as soon as the voice key was activated. Thus, it was possible to observe when the voice key was inappropriately activated by the S’s breath and whether the voice key was in fact activated by the first word of the phrase. The voice key mistriggered on approximately 4 percent of the trials, and these trials were eliminated from the analysis. Ss’ responses were tape recorded. Results Memorizution times Mean memorization times across phrases were obtained for each subject and entered into an 8 (contrast permutation)X2 (MS vs. MPP) analysis of variance for repeated measures. Error data were not included in the calculations of the means. Means rather than individual responses were analyzed in an attempt to constrain the variability of the data. The analysis showed a significant effect of permutation ( F(7, 56) = 1 I .84, p
[I] For each of the experiments reported, response latencies longer than 1.5 sets were eliminated from the means. These long scores, which constituted less than 4 percent of the data for each experiment. were eliminated because they fell at the extreme end of the distribution and probably represented disrupted processing or changes in strategy.
S. F. Ehrlich,
W. E. Cooper /
MEMORIZATION
I o
I 1
POSITIONS
I 3
I 2 OF
to prodwe
speech
131
TIMES
I I,2
CONTRASTING
RESPONSE
Re~pponse lutrnq
I
I 2,3
I,3
I 12.3
NOUNS
LATENCIES
800
-I 750
700
Y v)
s
650
550
5001
I 0
1 I
POSITIONS
I 3
I 2 OF
I
I
I
1,2
I,3
2.3
CONTRASTING
I 1,2,3
NOUNS
Fig. I. Mean memorization time and response latency-experiment
I
A Newman-Keuls analysis revealed that the significant differences lay between the condition with no substitutions and the other conditions and between the conditions with one substitution versus the conditions with more than one substitution (p
anulysis
Error responses included trials in which the Ss produced the wrong phrase, substituted or deleted words, or produced long hesitation pauses in the middle of phrases. Such errors constituted only 4 percent of the responses. None of these errors
were committed in phrases in which there were no contrasted words. Five percent of the one-contrast phrases contained errors, four percent of the two-contrast phrases contained errors, and eleven percent of the three-contrast phrases contained errors. Generally speaking, then, the number of errors was not inversely related to the number of contrasts, providing no evidence for a speed-accuracy trade-off. Discussion
The results of this experiment revealed that Ss were indeed able to take advantage of the commonality between the phrases during the memorization period and during the response latency interval. Apparently the Ss were able to store the information from the two phrases in an economical manner. Many of the Ss reported that they spent most of the memorization interval trying to memorize the contrasted words, and that they only needed to read through the common words briefly. Some of the Ss reported that they read the first phrase and then scanned through the second phrase for those words that were not the same as those in the first phrase, paying little or no attention to those words that were held in common. The fact that the response latencies increased with the number of contrasted words and were not simply dependent on the total length of the utterance suggests that contrast required some kind of independent processing during the planning of the utterance. Note that because some of the words were held in common between the phrases, planning of those words could have been done in advance of the prompt, thus the response latency may have reflected planning of just those words that were dictated by the prompt. Clearly, however, the S had some means of integrating the contrasted words with those words that were held in common between the phrases so that the output could be correctly sequenced [2]. The graph of the response latencies reveals that there was a tendency for responses to be longer when at least one of the contrasted words appeared in the first noun position than when there was no contrast in that position, although this effect was not found to be significant. This trend may reflect output of the first word when it was held in common, with planning of the contrasting words being delayed until later on. We have noted that the modifying relationship of the last prepositional phrase did not seem to affect either the memorization times or the response latencies. There was some theoretical motivation for expecting an effect for this syntactic variable. If we examine the experiment from the point of view of the task demands put on the S. it is clear that the he is required to remember which of the contrasted words go together, and our introspections suggest that there is a strong tendency to confuse the contrasted words. It was hypothesized that a modifying relationship might help the S to isolate the correct set of words for certain of the permutations. The strongest argument can be [2] An alternative account for the response latency result would be that the time needed to locate the first contrasted word increases with the load on short term memory (Stcrnbcrg IY6Y). Theoretically. the subject is only required to choose between one of two alternatives for the first word in the cases whcrc the initial words are contrasted. However. it remains a possibility that the load on STM may influence such binary decisions (Drewnowski IYXO). Given the highly structured organization of STM induced in this task. it is unclear whether results found with unstructured lihta would generalize to this task.
S. F. Ehrlic~h,W. E. Cooper / Response lutenq to produce speech
133
made for two cases where two of the words were contrasted. Consider first the case where the first and third nouns are contrasted, as in the following two examples: (1)
(T)
A casino with a gift shop in the basement
(B)
A museum with a gift shop in the lobby
(T)
A casino with a gift shop in the country
(B)
A museum with a gift shop in the city
(MPP)
(2)
(MH)
In the first case, where the last PP modifies the preceding PP (MPP), the contrasted words do not have a direct modifying relationship, but in the second case, where the last PP modifies the head noun (MH), the two words do bear a direct modifying relationship. In the case where the second and third nouns are contrasted, the opposite relationship holds. (3)
(4)
(T)
A casino with a gift shop in the basement
(B)
A casino with a snack bar in the lobby
(T)
A casino with a gift shop in the city
(B)
A casino with a snuck bar in the country
W’P)
In this case, the two contrasted words bear a direct modifying relationship in the MPP structure but not in the MS structure. If these modifying relationships are represented in the memory representation maintained by the Ss, then a direct relationship between contrasted words may help guide planning of the appropriate contrasted words. However, a number of counteracting factors could have occluded the importance of the modifying relationship for these Ss. Reexamination of the phrases revealed that, in some cases, words that did not have a direct syntactic link sometimes seemed to share semantic features (i.e. club house-polo shirt; wan-mailman), while some words which were syntactically linked were not very close in terms of semantic features (cusino-country; store-Utah). Another related problem was evident in the phrasessome of the words which did not have syntactic links had obvious functional relationships. This can clearly be seen in the cusino example. Although cusino is not directly modified by basement in the MPP structure, basement is clearly functionally related to the casino which contains it.
Experiment 2 In the second experiment, we attempted to insure that the semantic and functional relationships of the phrases were in accord with the syntactic structure. With this design, we could determine whether, taken together, the semantic, functional, and syntactic characteristics of modifying relationships would influence the time required for subjects to memorize and produce the phrases.
134
Method
Subjects Eight paid volunteers from the Harvard University community, three males and five females, participated in this experiment. None of these Ss had participated in experiment 1. Only Ss who were found to consistently trigger the voice key were tested.
Phrases consisting of a head noun and two prepositional phrases were developed. For each phrase pair, either the first and third nouns were contrasted between the phrases, or the second and third nouns were contrasted. Six phrase groups were developed independently for these two types. Within these types, the modifying relationship was varied by manipulating the last prepositional phrase, as illustrated in table 2. In cases where the last PP modified the head noun (MH), the phrases were also designed such that the last PP bore a close semantic relationship with the head noun but not with the preceding PP. In cases where the last PP modified the preceding PP (MPP), the two PP’s had a close semantic relationship, but the last PP did not have a close relationship with the head noun. Because particular MH and MPP phrase pairs were matched except for the last prepositional phrase, one member of the matched pair was assigned to one trial block and the other was assigned to a second trial block. The order of the trials was randomized within each trial block. Phrases developed for experiment 3 were randomly mixed with those for experiment 2 (see below). Half of the Ss saw the first trial block first and half saw the second trial block first. There were 24 practice trials and 24 experimental trials.
Table 2
Examples of phrase pairs used in experiment
2.
First and third nouns contrasted Last PP modifies
preceding
PP A nxwhk for the boy with a .swztun A letterfor the boy with a WCH’cut
(-0
(B) Last PP modifies
subject A nwrbke for the bov in the tq /mu A letter for the boy in the n~urlho.~
(T)
(B) Second and third nouns contrasted Last PP modifies
preceding
(-0 (B)
PP A note from the prrnc~q.wl of the sc~hool A note from the urchitec,t of the hour
Last PP modifies subject 0) (W
A note from theprrnc~pol on the (joot A note from the architect on the cur
Procedure Each S participated in one session which lasted approximately 45 min. The procedure was identical to that used for experiment 1, except for the total of three trial blocks-one practice, and two experimental. Results Memorirotion times The cases in which the first and third words contrasted were analyzed separately from the cases where the second and third words contrasted because the phrases were not matched across this variable. Again, means across phrases were examined statistically. The memorization time results are illustrated in fig. 2. Memorization times were found to be shorter when the contrasted words bore a strong modifying relationship both for the case where the first and third words were contrasted (MH) ( p
I
FIRST AND THIRDNOUN CONTRASTED
MODIFIES SlhJECT
TIME
I
MODIFIES PP
RESPONSE
MODIFIES SUBJECT
MODIFIES PP
LATENCY
FIRSTAND THIRD NOUN CONTRASTED 900
SECONDAND THIRDNOUN CONTRASTED
SECOND AND THIRD NOUN CONTRASTED 900
I
7001
MODIFIES SUBJECT
MODIFIES PP
Fig. 2. Mean memorization
7001
time and response
MODIFIES SUBJECT
MODIFIES PP
latency-experiment
2.
Response iutencles Response latencies were found to be shorter for cases where there was a direct modifying link between the contrasted words, but only when those words appeared in the first and third positions of the phrases (p
The response latency effect was not found for the cases where the second and third words were contrasted. Because the Ss knew in advance that the contrasted words would appear consecutively in the output, they may have been able to rely on directional pointers between those words that were created during the memorization phase, even though those words did not functionally modify each other in the MH condition. These directional pointers that dictate the output sequence would not have been useful in the condition where the contrasted word straddled a common noun, however, because the pointer from the first noun would lead to the noun that was held in common between the phrases and two competing pointers would lead away from that common node. There is a second explanation for the lack of effect of modifying relationship for the second and third noun contrasts. It is possible that planning of the contrasted words was delayed until the first word which was held in common between the phrases was spoken, clouding the importance of the modifying relationship. Future studies in which mid-production timing and pause durations are measured may provide clearer evidence for such delayed planning. (See Cooper and Paccia-Cooper 1980.) The fact that response latencies were generally shorter for both cases where the two contrasts occurred at the end of the phrase would be consistent with either of the explanations given above.
Experiment
3
In the third experiment, the effect of the semantic relationship between the contrasted words was evaluated while the syntactic structure of the phrase was held constant. The trials for this experiment were intermixed with those of experiment 2, although the phrases were developed independently. Phrases with related and unrelated contrasts in the first and third positions and phrases with such contrasts in the second and third positions were developed. The contrasted words in the phrases did not have a direct modifying relationship to each other in their most likely interpretation. Example phrases are given in table 3. Results Memorization times Again, the cases where the first and third nouns contrasted were analyzed separately from the cases where the second and third nouns contrasted. The results are illustrated in fig. 3. Memorization times were found to be shorter when there was a close semantic relationship between the contrasted words, both for the cases where the first and third nouns were contrasted (~~0.01, t= 3.24, df= 7) and for the cases where the second and third nouns were contrasted (pcO.05, t = 2.30, df = 7). Response latency The response latency results paralleled the results found in experiment 2, with only the cases with contrasts in the first and third positions showing an advantage of the semantic relationship (pcO.05, t = 2.39, df= 7).
Table 3 Examples
of phrase
pairs used in experiment
3.
First and third nouns contrasted Related A &urr.vr near the room with the X-rc~~,., A /nl&r near the room with the wrtdwv
(T) 0% Unrelated
A dwtr.stnearthe room Hith the rw ho.~ A /CMekv near the room with thcf/,uwui
CT) (B)
Second and third nouns contrasted Related 0) (B) Unrelated (T) (B)
MEMORIZATION
I
TIME
FIRST AND THIRD NOUN CONTRASTED
RELATED
I
UNRELATED
RESPONSE
RELATED
UNRELATED
LATENCY
FIRST AND THIRD NOUN
_sI-_
SECOND AND THIRD NOUN CONTRASTED
SECOND AND THIRD NOUN
j:':-
RELATED
UNRELATED
Fig. 3. Mean memorization
time and response
RELATED
UNRELATED
latency-experiment
3
Errors
Six percent of the errors independent of where the first and association contained contained errors.
cases where the second the degree of relatedness third words contrasted, errors while 4 percent
and third words contrasted contained of the contrasted words. For the cases two percent of the cases with close of the cases with unrelated contrasts
Discussion
The strength of the semantic relationship independently affect both memorization that this kind of relationship is useful words that are stored in a complex messages. It remains to be seen whether regardless of the semantic relationships
between two contrasted words apparently can time and response latency. It therefore appears for the activation of production commands for memory representation that encompasses two a syntactic link would serve the same function involved.
General discussion of experiment 1 showed that both memorization time and response latency were dependent on the relationship between two possible linguistic responses. Memorization took less time as the number of nouns that were shared between the phrases increased. Response latency seemed to be tied to processing of the contrasted words, perhaps because words held in common between the phrases could be planned, in some sense, in advance of the prompt. It has been suggested that the subject must have available information about the relative sequence of the contrasted and common words in order to produce the correct output, and a network representation has been suggested as providing that information. Note that the results found here may generalize to the production of non-linguistic strings for which the same processing apparatus might be used. The results of the second and third experiments have demonstrated that subjects can take advantage of modifying and semantic relationships between the contrasted words to speed up both memorization time and response latency. These results imply that the subjects were using a meaningful interpretation of the phrases to help in memorizing them. We must consider the degree to which the strategies employed by the subjects in this task are relevant to natural speech production. The subjects seemed to process the contrasted words separately from common material at some level and this kind or processing strategy is not generally consistent with models of speech planning which presume that each sentence is planned in a top-down, left to right sequence (see Butterworth 1980; Clark and Clark 1977; Fodor et al. 1974). It is possible that this strategy is task specific, and cannot be taken to reflect the nature of memory representation and speech planning in
The results
natural conversations. Subjects may, for example, have depended on memory of the visual configuration of the screen to help them sequence the words. Future experiments in which the memorized material is obtained in the auditory mode will be useful in testing the generalizabihty of the results. We would like to tentatively suggest, however, that this task does address some processing issues that are not easily examined under conditions where unrelated sentences are memorized. It seems that it is often the case that we select the content of a sentence in stages. For example, we might first decide to describe buildings that have snack bars in conventional locations. We might then decide to describe a particular instance such as ‘a museum with a snack bar in the basement’. It seems reasonable to assume that the concept ‘snack bar’ is designated in memory for output in advance of the concepts ‘museum’ and ‘basement’. It also seems reasonable that search for the second set of concepts would be dependent on the semantic relationships (including modifying relationships) between them. If speech planning is done in this piecemeal fashion, then the present paradigm provides a means for examining these content selection and sequenching procedures because it provides the subject with more than a single sentence worth of information to select from. (See also Cooper and Ehrlich 198 1.) Under more natural conditions, the two potential messages would be embedded in a larger context, and links between contrasted words would likely exist, at least indirectly, even when the concepts involved would not directly modify each other. The content of one message might have occurred at one time during the day, and the content of the other message might have occurred at another time. Thus “time of day” would be the criterion for selecting and activating the appropriate nodes rather than the rather arbitrary “top” vs. “bottom” cues used in this experiment. Morton (1970) has suggested that the content of an utterance is loaded into a response buffer which is then used as the basis for the execution of speech. This buffer has capacity limitations and has been recently described as isomorphic with short term memory by Ellis (1979. 1980). The idea that speech production requires activation of nodes within a memory representation may be more consistent with the response buffer conceptualization than it first appears. Instead of being a separate structure, the buffer may be created via the pattern of priming created within the memory structure. Capacity limitations can thus be seen as limitations in the number of nodes that can be simultaneously primed for output. Morton and Smith (1974) have assumed that the content of the response buffer is serially organized. Again, we must have some means of representing the serial ordering of the activated nodes for output in our model, and it has been suggested above that speakers may be able to employ directional pointers dictating serial order. These directional pointers must be superimposed on the propositional network in order to allow for the creation of sequences for consecutively ordered items that are not
directly linked within the propositional structure. These pointers would allow correct sequencing of the MH phrases in the current set of experiments, where two unlinked prepositions appear consecutively. It is possible that these directional pointers could be set up during the memorization period and used to guide the activation of the correct nodes once the prompt is received designating the correct subset to be employed. For example, the prompt may be associated with the first of the two contrasted words within the sentence. Access of the first word would in turn prime the second via the directional pointer between them. Such directional pointers would not be useful in the MPP condition where the first and third nouns are contrasted, however, because the first pointer would by necessity lead to the common material that occurs in the middle of the output sequence, providing no means for “selecting” the appropriate word at the end of the phrase. The relative usefulness of these directional pointers for activating the correct contrasted words would dictate whether or not the subject would need to rely on the modifying relationships between the contrasted words to guide activation of those nodes. We emphasize that the suggestions made concerning the nature of the representation used under the conditions of these experiments should be considered tentative. However, preproduction content decisions have also been demonstrated by Lindsey (1975, 1976) in a task where subjects are asked to produce descriptions of pictures, where some of the content of the pictures is known to the subject in advance. Both of these methods may be useful in specifying the means by which content selection is orchestrated in relation to other aspects of production.
References Anderson, J.R.. 1976. Language, memory and thought. Hillsdale, NJ: Erlbaum. Anderson, J.R. and G.H. Bower, 1973. Human associative memory. Washington, DC: Winston and Sons. Bransford, J.D. and J.J. Franks, 1971. The abstraction of linguistic ideas. Cognitive Psychology 2. 331-350. Butterworth. B., 1980. Language production, Vol. I: Speech and talk. London: Academic Press. Clark. H.H. and E.V. Clark, 1977. Psychology and language: an introduction to psycholinguistics. New York: Harcourt: Brace, Jovanovich. Cooper, W.E. and S.F. Ehrlich, 1981. ‘Planning speech: studies in choice reaction time’. In: A. Baddeley and J. Long (eds.). Attention and performance IX. Hillsdale. NJ: Erlbaum (in press). Cooper, W.E. and J. Paccia-Cooper. 1980. Syntax and speech. Cambridge. MA: Harvard Univcrsity Press. Drewnowski, A., 1980. Attributes and priorities in short-term recall: a new model of memory span. Journal of Experimental Psychology: General 109 (2). 208-250. Ellis, A.W., 1979. ‘Speech production and short-term memory’. In: J. Morton and J.C. Marshall (eds.), Psycholinguistic series, Vol. 2: Structures and processes. Cambridge, MA: MIT Press. Ellis, A.W.. 1980. Errors in speech and short-term memory: the effects of phonemic similarity and syllable position. Journal of Verbal Learning and Verbal Behavior 19. 624-634.
Fodor. J.A., T.G. Bever and M.F. Garrett. 1974. The psychology of language. New York: McGraw-Hill. Huggins, A.W.F., 1969. A facility for studying perception of timing in natural speech. Quartcrl~ Progress Report of the MIT Research Laboratoy of Electronic5 9.5. 8 I -X3. Klapp, S.T., 1979. ‘Reaction time analysis of programmed control’. In: R. Hutton (cd.). Excrciw and sports science reviews. Santa Barbara. CA: Journal Publishing Affiliates. Lindsey. J.R.. lY75. Producing simple utterances: how far ahead do wc plan? Cognitive Psychology 7. l-19. Lindsey. J.R., 1976. Producing simple utterances: details of the planning process. Journal of Psycholinguistic Research 5. 33 l-354. Morton, J., 1970. ‘A functional model for memory’. In: D.A. Norman (cd.), Models of human memory. New York: Academic Press. Morton, J. and N.V. Smith, 1974. Some ideas concerning the acquisition of phonology. In: Proceedings of the symposium on current problems in paycholinguistica. Paris: CNRS. Norman, D.A., D.E. Rummclhart and the LNR Research Group. lY75. Ezplorationa in cognition. San Francisco, CA: Freeman. Sternberg, S.. 1969. Memoryscanning: mental procesxs revcalcd by reaction-time experiments. American Scientist 57 (4). 421-457.
MEMORY DETERMINANTS SPEECH * Susan F. EHRLICH
and William
127
OF RESPONSE
LATENCY
TO PRODUCE
E. COOPER
I~arocrrdU~~roers~!,: USA Accepted
May 1981
In three experiments, subjects were asked to memorize related phrase pairs and then to produce one of these phrases from a cue. In Experiment 1, it was found that both memorization times and response latencies increased with the number of words that differed between the phrases. In Experiment 2 and 3. it was shown that the presence of a strong modifying or semantic relationship between words in one phrase influenced both memorization time and response latency when those same words were contrasted between the two phrases. The implications of the results for models of storage, retrieval, and planning of speech are considered.
In this paper a new approach for studying response latency to produce speech is described. Subjects were presented with two noun phrases to memorize. The phrases were associated to prompts during the memorization interval, and subjects were instructed to produce one of the phrases after receiving a prompt. The use of only two potential responses has generally been avoided in response latency experiments because of the possibility that subjects may anticipate one of the responses, thus influencing the type of processing occurring in the response latency interval and adding to latency variability has yielded (Klapp 1979). We have found, however, that this procedure significant effects, overriding response variability, that allow us to gain information about speech planning operations that are dependent on the relationship between the two potential responses. In the first experiment, both potential responses contained a head noun and two prepositional phrases. The number of nouns that were shared between the phrases was varied between 0 and 3. The amount of time required to memorize the phrases was recorded as well as the response latency to initiate production of one of the phrases from the prompt. Pilot data had suggested that subjects * This work was supported by NIH Grant NS-15059. We thank Scott Bradner and the Computer Based Laboratory at Harvard for facilities and programming. In addition, we thank Trude Huber for help in running SUbJects and providing suggestions. Mailing address: SF. Ehrlich. 1202 William James Hall, Dept. of Psychology and Social Relations, Harvard University, 33 Kirkland Street, Cambridge, MA 02138. USA. 0001-69 18/82/0000~0000/$02.75
0 1982 North-Holland
were
able to take advantage
memorization interval experiment was a first
of the commonality
of the phrases
both
during
the
and during the response latency interval, and this attempt to examine the advantage of the commonality
formally.
Experiment
1
Method SubJects
Nine members of the Harvard University community, one male and eight females, participated as paid volunteers in the experiment. Three other Ss were eliminated because of their inability to consistently trigger the reaction time equipment used in the experiment, and two other Ss were eliminated before any statistical analyses were carried out because of their unusually long response latencies. Muterids Six phrase groups were developed. Each phrase consisted of a head noun and two prepositional phrases. For each phrase group there were two base phrases, and the eight experimental conditions (having identical stress patterns) were derived from these base phrases. Each phrase started with the word “A” because the vowel was found to be a more consistent trigger for the voice key than another candidate word, “The”, which begins with a low amplitude fricative. The base phrases are listed in table 1. During an experimental trial, the S was asked to memorize two of the phrases derived from the base phrases. The two phrases were either (I) identical, (2) differing in terms of one noun, (3) differing in terms of two nouns or (4) differing in terms of all
Table I Base phrases
used to generate
phrase
pairs in experiment
1
Set I
A photo of a bush in the garden (bedroom) A drawing of a tree in the valley (hallway)
Set 2
A girl in a van with a bike rack (mailman) A man in a car with a sunroof (robber)
set 3
A casino with a gift shop in the lobby (country) A museum with a snack bar in the basement (city)
Set 4
A truck with olives in barrels (Texas) A store with pickles in bottles (Utah)
Set 5
A lawyer in the mansion with a swimming pool (leisure suit) A doctor in the clubhouse with a sauna bath (polo shirt)
Set 6
A novel about mountains in Poland (Hilles) A pamphlet about rivers in England (Widener)
three nouns. The locations of the contrasting words were varied systematically, resulting in eight permutations. A second independent variable was superimposed on these eight types of pairs. The last prepositional phrase in the noun phrase either modified the head noun (MH) or the noun in the preceding prepositional phrase (MPP), resulting in 16 different conditions for each of the six base pairs. The phrases with the MH structure were identical to the phrases with the MPP structure except for the last noun. The nouns used for the MH structures are presented in parentheses in table 1. It should be noted here that while an effort was made to make the two different modifying structures as distinct as possible, the phrases were still potentially ambiguous, particularly if the Ss elected to encode absurd interpretations such as “(A man in a car) with a sunroof”. Equipment
The Ss were seated in front of a cathode ray tube that was controlled by a PDP-4 Computer. New trials were triggered by the S with a button. Ss wore headphones and spoke into a microphone which fed into a Grason-Stadler voice key (Model no. E7300-Al). The appropriateness of the onset delay setting and the gain setting for the voice key was examined visually using the AUDITS computer program (Huggins 1969). With this program, it was possible to measure the time delay between the onset of the precue beep and the onset of the waveform of the S’s voice, displayed on a CRT. Procedure
Each S participated individually in one session with an average duration of 90 min. When the S entered the experimental room, he was seated in front of the cathode ray tube, and the procedure was described. The experiment consisted of a series of 96 trials. Each of the 96 trials was randomly assigned to one of three blocks, and the order of the trials within the blocks was randomized. The location of a particular phrase in the top or bottom of the display was randomized, and the use of a Top vs. Bottom cue for particular trials was chosen at random. All Ss saw the same three trial blocks, but the order of the blocks was rotated for the nine Ss. The test trials were preceded by a practice block of 24 trials. Ss were given breaks after each trial block. On each trial, two phrases appeared on the screen, one on the top with a “T” printed in front if it and one on the bottom with a “B” in front of it. Ss were told to take as much as they needed to memorize the phrases and to signal their completion of the memorization phase by pressing a button. At that point, the phrases disappeared from the screen, followed by a one second period. A precue beep was then presented over the headphones. A second later, a cue appeared on the screen. The cue was either a “T” or a “B”, and the letter was positioned in the same location as the original “T” or “B” had been when the phrases still appeared on the screen. The Ss were instructed to produce the phrase that corresponded to the letter as quickly as possible into the microphone. This general instruction was given only once in an attempt to induce differential response latencies. However, no special premium was placed on either speed of production or speed of response initiation during the experimental session. Ss’ utterances appeared to fall within a normal range of speaking rates. The S then pushed a button to start the next trial. The amount of time the S spent looking at each phrase pair (memorization time) and the period between the onset of the cue and the onset of the S’s voice (response latency) were recorded by the computer.
Ss were instructed to speak clearly, to avoid extraneous activity during the memorization period, and to avoid errors. Cash bonuses were given for accuracy. Ss were also cautioned not to use any unusual mnemonic strategies to help them remember the phrases. During the experimental session, the experimenter monitored the Ss’ responses and wrote down any errors. At the same time, the experimenter watched the screen to observe when the “T” or “B” cue disappeared. The computer had been programmed to terminate display of the cue as soon as the voice key was activated. Thus, it was possible to observe when the voice key was inappropriately activated by the S’s breath and whether the voice key was in fact activated by the first word of the phrase. The voice key mistriggered on approximately 4 percent of the trials, and these trials were eliminated from the analysis. Ss’ responses were tape recorded. Results Memorizution times Mean memorization times across phrases were obtained for each subject and entered into an 8 (contrast permutation)X2 (MS vs. MPP) analysis of variance for repeated measures. Error data were not included in the calculations of the means. Means rather than individual responses were analyzed in an attempt to constrain the variability of the data. The analysis showed a significant effect of permutation ( F(7, 56) = 1 I .84, p
[I] For each of the experiments reported, response latencies longer than 1.5 sets were eliminated from the means. These long scores, which constituted less than 4 percent of the data for each experiment. were eliminated because they fell at the extreme end of the distribution and probably represented disrupted processing or changes in strategy.
S. F. Ehrlich,
W. E. Cooper /
MEMORIZATION
I o
I 1
POSITIONS
I 3
I 2 OF
to prodwe
speech
131
TIMES
I I,2
CONTRASTING
RESPONSE
Re~pponse lutrnq
I
I 2,3
I,3
I 12.3
NOUNS
LATENCIES
800
-I 750
700
Y v)
s
650
550
5001
I 0
1 I
POSITIONS
I 3
I 2 OF
I
I
I
1,2
I,3
2.3
CONTRASTING
I 1,2,3
NOUNS
Fig. I. Mean memorization time and response latency-experiment
I
A Newman-Keuls analysis revealed that the significant differences lay between the condition with no substitutions and the other conditions and between the conditions with one substitution versus the conditions with more than one substitution (p
anulysis
Error responses included trials in which the Ss produced the wrong phrase, substituted or deleted words, or produced long hesitation pauses in the middle of phrases. Such errors constituted only 4 percent of the responses. None of these errors
were committed in phrases in which there were no contrasted words. Five percent of the one-contrast phrases contained errors, four percent of the two-contrast phrases contained errors, and eleven percent of the three-contrast phrases contained errors. Generally speaking, then, the number of errors was not inversely related to the number of contrasts, providing no evidence for a speed-accuracy trade-off. Discussion
The results of this experiment revealed that Ss were indeed able to take advantage of the commonality between the phrases during the memorization period and during the response latency interval. Apparently the Ss were able to store the information from the two phrases in an economical manner. Many of the Ss reported that they spent most of the memorization interval trying to memorize the contrasted words, and that they only needed to read through the common words briefly. Some of the Ss reported that they read the first phrase and then scanned through the second phrase for those words that were not the same as those in the first phrase, paying little or no attention to those words that were held in common. The fact that the response latencies increased with the number of contrasted words and were not simply dependent on the total length of the utterance suggests that contrast required some kind of independent processing during the planning of the utterance. Note that because some of the words were held in common between the phrases, planning of those words could have been done in advance of the prompt, thus the response latency may have reflected planning of just those words that were dictated by the prompt. Clearly, however, the S had some means of integrating the contrasted words with those words that were held in common between the phrases so that the output could be correctly sequenced [2]. The graph of the response latencies reveals that there was a tendency for responses to be longer when at least one of the contrasted words appeared in the first noun position than when there was no contrast in that position, although this effect was not found to be significant. This trend may reflect output of the first word when it was held in common, with planning of the contrasting words being delayed until later on. We have noted that the modifying relationship of the last prepositional phrase did not seem to affect either the memorization times or the response latencies. There was some theoretical motivation for expecting an effect for this syntactic variable. If we examine the experiment from the point of view of the task demands put on the S. it is clear that the he is required to remember which of the contrasted words go together, and our introspections suggest that there is a strong tendency to confuse the contrasted words. It was hypothesized that a modifying relationship might help the S to isolate the correct set of words for certain of the permutations. The strongest argument can be [2] An alternative account for the response latency result would be that the time needed to locate the first contrasted word increases with the load on short term memory (Stcrnbcrg IY6Y). Theoretically. the subject is only required to choose between one of two alternatives for the first word in the cases whcrc the initial words are contrasted. However. it remains a possibility that the load on STM may influence such binary decisions (Drewnowski IYXO). Given the highly structured organization of STM induced in this task. it is unclear whether results found with unstructured lihta would generalize to this task.
S. F. Ehrlic~h,W. E. Cooper / Response lutenq to produce speech
133
made for two cases where two of the words were contrasted. Consider first the case where the first and third nouns are contrasted, as in the following two examples: (1)
(T)
A casino with a gift shop in the basement
(B)
A museum with a gift shop in the lobby
(T)
A casino with a gift shop in the country
(B)
A museum with a gift shop in the city
(MPP)
(2)
(MH)
In the first case, where the last PP modifies the preceding PP (MPP), the contrasted words do not have a direct modifying relationship, but in the second case, where the last PP modifies the head noun (MH), the two words do bear a direct modifying relationship. In the case where the second and third nouns are contrasted, the opposite relationship holds. (3)
(4)
(T)
A casino with a gift shop in the basement
(B)
A casino with a snack bar in the lobby
(T)
A casino with a gift shop in the city
(B)
A casino with a snuck bar in the country
W’P)
In this case, the two contrasted words bear a direct modifying relationship in the MPP structure but not in the MS structure. If these modifying relationships are represented in the memory representation maintained by the Ss, then a direct relationship between contrasted words may help guide planning of the appropriate contrasted words. However, a number of counteracting factors could have occluded the importance of the modifying relationship for these Ss. Reexamination of the phrases revealed that, in some cases, words that did not have a direct syntactic link sometimes seemed to share semantic features (i.e. club house-polo shirt; wan-mailman), while some words which were syntactically linked were not very close in terms of semantic features (cusino-country; store-Utah). Another related problem was evident in the phrasessome of the words which did not have syntactic links had obvious functional relationships. This can clearly be seen in the cusino example. Although cusino is not directly modified by basement in the MPP structure, basement is clearly functionally related to the casino which contains it.
Experiment 2 In the second experiment, we attempted to insure that the semantic and functional relationships of the phrases were in accord with the syntactic structure. With this design, we could determine whether, taken together, the semantic, functional, and syntactic characteristics of modifying relationships would influence the time required for subjects to memorize and produce the phrases.
134
Method
Subjects Eight paid volunteers from the Harvard University community, three males and five females, participated in this experiment. None of these Ss had participated in experiment 1. Only Ss who were found to consistently trigger the voice key were tested.
Phrases consisting of a head noun and two prepositional phrases were developed. For each phrase pair, either the first and third nouns were contrasted between the phrases, or the second and third nouns were contrasted. Six phrase groups were developed independently for these two types. Within these types, the modifying relationship was varied by manipulating the last prepositional phrase, as illustrated in table 2. In cases where the last PP modified the head noun (MH), the phrases were also designed such that the last PP bore a close semantic relationship with the head noun but not with the preceding PP. In cases where the last PP modified the preceding PP (MPP), the two PP’s had a close semantic relationship, but the last PP did not have a close relationship with the head noun. Because particular MH and MPP phrase pairs were matched except for the last prepositional phrase, one member of the matched pair was assigned to one trial block and the other was assigned to a second trial block. The order of the trials was randomized within each trial block. Phrases developed for experiment 3 were randomly mixed with those for experiment 2 (see below). Half of the Ss saw the first trial block first and half saw the second trial block first. There were 24 practice trials and 24 experimental trials.
Table 2
Examples of phrase pairs used in experiment
2.
First and third nouns contrasted Last PP modifies
preceding
PP A nxwhk for the boy with a .swztun A letterfor the boy with a WCH’cut
(-0
(B) Last PP modifies
subject A nwrbke for the bov in the tq /mu A letter for the boy in the n~urlho.~
(T)
(B) Second and third nouns contrasted Last PP modifies
preceding
(-0 (B)
PP A note from the prrnc~q.wl of the sc~hool A note from the urchitec,t of the hour
Last PP modifies subject 0) (W
A note from theprrnc~pol on the (joot A note from the architect on the cur
Procedure Each S participated in one session which lasted approximately 45 min. The procedure was identical to that used for experiment 1, except for the total of three trial blocks-one practice, and two experimental. Results Memorirotion times The cases in which the first and third words contrasted were analyzed separately from the cases where the second and third words contrasted because the phrases were not matched across this variable. Again, means across phrases were examined statistically. The memorization time results are illustrated in fig. 2. Memorization times were found to be shorter when the contrasted words bore a strong modifying relationship both for the case where the first and third words were contrasted (MH) ( p
I
FIRST AND THIRDNOUN CONTRASTED
MODIFIES SlhJECT
TIME
I
MODIFIES PP
RESPONSE
MODIFIES SUBJECT
MODIFIES PP
LATENCY
FIRSTAND THIRD NOUN CONTRASTED 900
SECONDAND THIRDNOUN CONTRASTED
SECOND AND THIRD NOUN CONTRASTED 900
I
7001
MODIFIES SUBJECT
MODIFIES PP
Fig. 2. Mean memorization
7001
time and response
MODIFIES SUBJECT
MODIFIES PP
latency-experiment
2.
Response iutencles Response latencies were found to be shorter for cases where there was a direct modifying link between the contrasted words, but only when those words appeared in the first and third positions of the phrases (p
The response latency effect was not found for the cases where the second and third words were contrasted. Because the Ss knew in advance that the contrasted words would appear consecutively in the output, they may have been able to rely on directional pointers between those words that were created during the memorization phase, even though those words did not functionally modify each other in the MH condition. These directional pointers that dictate the output sequence would not have been useful in the condition where the contrasted word straddled a common noun, however, because the pointer from the first noun would lead to the noun that was held in common between the phrases and two competing pointers would lead away from that common node. There is a second explanation for the lack of effect of modifying relationship for the second and third noun contrasts. It is possible that planning of the contrasted words was delayed until the first word which was held in common between the phrases was spoken, clouding the importance of the modifying relationship. Future studies in which mid-production timing and pause durations are measured may provide clearer evidence for such delayed planning. (See Cooper and Paccia-Cooper 1980.) The fact that response latencies were generally shorter for both cases where the two contrasts occurred at the end of the phrase would be consistent with either of the explanations given above.
Experiment
3
In the third experiment, the effect of the semantic relationship between the contrasted words was evaluated while the syntactic structure of the phrase was held constant. The trials for this experiment were intermixed with those of experiment 2, although the phrases were developed independently. Phrases with related and unrelated contrasts in the first and third positions and phrases with such contrasts in the second and third positions were developed. The contrasted words in the phrases did not have a direct modifying relationship to each other in their most likely interpretation. Example phrases are given in table 3. Results Memorization times Again, the cases where the first and third nouns contrasted were analyzed separately from the cases where the second and third nouns contrasted. The results are illustrated in fig. 3. Memorization times were found to be shorter when there was a close semantic relationship between the contrasted words, both for the cases where the first and third nouns were contrasted (~~0.01, t= 3.24, df= 7) and for the cases where the second and third nouns were contrasted (pcO.05, t = 2.30, df = 7). Response latency The response latency results paralleled the results found in experiment 2, with only the cases with contrasts in the first and third positions showing an advantage of the semantic relationship (pcO.05, t = 2.39, df= 7).
Table 3 Examples
of phrase
pairs used in experiment
3.
First and third nouns contrasted Related A &urr.vr near the room with the X-rc~~,., A /nl&r near the room with the wrtdwv
(T) 0% Unrelated
A dwtr.stnearthe room Hith the rw ho.~ A /CMekv near the room with thcf/,uwui
CT) (B)
Second and third nouns contrasted Related 0) (B) Unrelated (T) (B)
MEMORIZATION
I
TIME
FIRST AND THIRD NOUN CONTRASTED
RELATED
I
UNRELATED
RESPONSE
RELATED
UNRELATED
LATENCY
FIRST AND THIRD NOUN
_sI-_
SECOND AND THIRD NOUN CONTRASTED
SECOND AND THIRD NOUN
j:':-
RELATED
UNRELATED
Fig. 3. Mean memorization
time and response
RELATED
UNRELATED
latency-experiment
3
Errors
Six percent of the errors independent of where the first and association contained contained errors.
cases where the second the degree of relatedness third words contrasted, errors while 4 percent
and third words contrasted contained of the contrasted words. For the cases two percent of the cases with close of the cases with unrelated contrasts
Discussion
The strength of the semantic relationship independently affect both memorization that this kind of relationship is useful words that are stored in a complex messages. It remains to be seen whether regardless of the semantic relationships
between two contrasted words apparently can time and response latency. It therefore appears for the activation of production commands for memory representation that encompasses two a syntactic link would serve the same function involved.
General discussion of experiment 1 showed that both memorization time and response latency were dependent on the relationship between two possible linguistic responses. Memorization took less time as the number of nouns that were shared between the phrases increased. Response latency seemed to be tied to processing of the contrasted words, perhaps because words held in common between the phrases could be planned, in some sense, in advance of the prompt. It has been suggested that the subject must have available information about the relative sequence of the contrasted and common words in order to produce the correct output, and a network representation has been suggested as providing that information. Note that the results found here may generalize to the production of non-linguistic strings for which the same processing apparatus might be used. The results of the second and third experiments have demonstrated that subjects can take advantage of modifying and semantic relationships between the contrasted words to speed up both memorization time and response latency. These results imply that the subjects were using a meaningful interpretation of the phrases to help in memorizing them. We must consider the degree to which the strategies employed by the subjects in this task are relevant to natural speech production. The subjects seemed to process the contrasted words separately from common material at some level and this kind or processing strategy is not generally consistent with models of speech planning which presume that each sentence is planned in a top-down, left to right sequence (see Butterworth 1980; Clark and Clark 1977; Fodor et al. 1974). It is possible that this strategy is task specific, and cannot be taken to reflect the nature of memory representation and speech planning in
The results
natural conversations. Subjects may, for example, have depended on memory of the visual configuration of the screen to help them sequence the words. Future experiments in which the memorized material is obtained in the auditory mode will be useful in testing the generalizabihty of the results. We would like to tentatively suggest, however, that this task does address some processing issues that are not easily examined under conditions where unrelated sentences are memorized. It seems that it is often the case that we select the content of a sentence in stages. For example, we might first decide to describe buildings that have snack bars in conventional locations. We might then decide to describe a particular instance such as ‘a museum with a snack bar in the basement’. It seems reasonable to assume that the concept ‘snack bar’ is designated in memory for output in advance of the concepts ‘museum’ and ‘basement’. It also seems reasonable that search for the second set of concepts would be dependent on the semantic relationships (including modifying relationships) between them. If speech planning is done in this piecemeal fashion, then the present paradigm provides a means for examining these content selection and sequenching procedures because it provides the subject with more than a single sentence worth of information to select from. (See also Cooper and Ehrlich 198 1.) Under more natural conditions, the two potential messages would be embedded in a larger context, and links between contrasted words would likely exist, at least indirectly, even when the concepts involved would not directly modify each other. The content of one message might have occurred at one time during the day, and the content of the other message might have occurred at another time. Thus “time of day” would be the criterion for selecting and activating the appropriate nodes rather than the rather arbitrary “top” vs. “bottom” cues used in this experiment. Morton (1970) has suggested that the content of an utterance is loaded into a response buffer which is then used as the basis for the execution of speech. This buffer has capacity limitations and has been recently described as isomorphic with short term memory by Ellis (1979. 1980). The idea that speech production requires activation of nodes within a memory representation may be more consistent with the response buffer conceptualization than it first appears. Instead of being a separate structure, the buffer may be created via the pattern of priming created within the memory structure. Capacity limitations can thus be seen as limitations in the number of nodes that can be simultaneously primed for output. Morton and Smith (1974) have assumed that the content of the response buffer is serially organized. Again, we must have some means of representing the serial ordering of the activated nodes for output in our model, and it has been suggested above that speakers may be able to employ directional pointers dictating serial order. These directional pointers must be superimposed on the propositional network in order to allow for the creation of sequences for consecutively ordered items that are not
directly linked within the propositional structure. These pointers would allow correct sequencing of the MH phrases in the current set of experiments, where two unlinked prepositions appear consecutively. It is possible that these directional pointers could be set up during the memorization period and used to guide the activation of the correct nodes once the prompt is received designating the correct subset to be employed. For example, the prompt may be associated with the first of the two contrasted words within the sentence. Access of the first word would in turn prime the second via the directional pointer between them. Such directional pointers would not be useful in the MPP condition where the first and third nouns are contrasted, however, because the first pointer would by necessity lead to the common material that occurs in the middle of the output sequence, providing no means for “selecting” the appropriate word at the end of the phrase. The relative usefulness of these directional pointers for activating the correct contrasted words would dictate whether or not the subject would need to rely on the modifying relationships between the contrasted words to guide activation of those nodes. We emphasize that the suggestions made concerning the nature of the representation used under the conditions of these experiments should be considered tentative. However, preproduction content decisions have also been demonstrated by Lindsey (1975, 1976) in a task where subjects are asked to produce descriptions of pictures, where some of the content of the pictures is known to the subject in advance. Both of these methods may be useful in specifying the means by which content selection is orchestrated in relation to other aspects of production.
References Anderson, J.R.. 1976. Language, memory and thought. Hillsdale, NJ: Erlbaum. Anderson, J.R. and G.H. Bower, 1973. Human associative memory. Washington, DC: Winston and Sons. Bransford, J.D. and J.J. Franks, 1971. The abstraction of linguistic ideas. Cognitive Psychology 2. 331-350. Butterworth. B., 1980. Language production, Vol. I: Speech and talk. London: Academic Press. Clark. H.H. and E.V. Clark, 1977. Psychology and language: an introduction to psycholinguistics. New York: Harcourt: Brace, Jovanovich. Cooper, W.E. and S.F. Ehrlich, 1981. ‘Planning speech: studies in choice reaction time’. In: A. Baddeley and J. Long (eds.). Attention and performance IX. Hillsdale. NJ: Erlbaum (in press). Cooper, W.E. and J. Paccia-Cooper. 1980. Syntax and speech. Cambridge. MA: Harvard Univcrsity Press. Drewnowski, A., 1980. Attributes and priorities in short-term recall: a new model of memory span. Journal of Experimental Psychology: General 109 (2). 208-250. Ellis, A.W., 1979. ‘Speech production and short-term memory’. In: J. Morton and J.C. Marshall (eds.), Psycholinguistic series, Vol. 2: Structures and processes. Cambridge, MA: MIT Press. Ellis, A.W.. 1980. Errors in speech and short-term memory: the effects of phonemic similarity and syllable position. Journal of Verbal Learning and Verbal Behavior 19. 624-634.
Fodor. J.A., T.G. Bever and M.F. Garrett. 1974. The psychology of language. New York: McGraw-Hill. Huggins, A.W.F., 1969. A facility for studying perception of timing in natural speech. Quartcrl~ Progress Report of the MIT Research Laboratoy of Electronic5 9.5. 8 I -X3. Klapp, S.T., 1979. ‘Reaction time analysis of programmed control’. In: R. Hutton (cd.). Excrciw and sports science reviews. Santa Barbara. CA: Journal Publishing Affiliates. Lindsey. J.R.. lY75. Producing simple utterances: how far ahead do wc plan? Cognitive Psychology 7. l-19. Lindsey. J.R., 1976. Producing simple utterances: details of the planning process. Journal of Psycholinguistic Research 5. 33 l-354. Morton, J., 1970. ‘A functional model for memory’. In: D.A. Norman (cd.), Models of human memory. New York: Academic Press. Morton, J. and N.V. Smith, 1974. Some ideas concerning the acquisition of phonology. In: Proceedings of the symposium on current problems in paycholinguistica. Paris: CNRS. Norman, D.A., D.E. Rummclhart and the LNR Research Group. lY75. Ezplorationa in cognition. San Francisco, CA: Freeman. Sternberg, S.. 1969. Memoryscanning: mental procesxs revcalcd by reaction-time experiments. American Scientist 57 (4). 421-457.