Acoustic factors versus language factors
in short-term memory!

R. CONRAD, P. R. FREEMAN AND A. J. HULL
MED ICAL RESEARCH COUNCIL, APPLIED PSYCHOLOGY RESEARCH UN I T , CA MB RIDGE , EN GL AND

Ablitract

Forty five Ss recalled 6-consonant sequenc es im-
mediately afte r letter by letter visual presentation. The

main factor contributing to ea se of r ecall was withi n-
seque nce ac oustic confusability . Language habits we re

r el ati vel y unimportant. Single - letter language fre-
quen cy was unrelated to r ecall; second order effec ts

made a small but significant contr ibuti on.
In troduc tlon
One of the r easons why Ebbinghau s thought so highly
of nons ense syllables was the belief that they would
be free from me aning and the effec ts of language

expe r ie nce; memory could thu s be studied uncon-
taminated by verbal habit. That the a s su mption was

fal se ha s long been r ecognised, and for 40 year s or
more no ve rba l learning expe rime nts have used nonsense
syllables without contr olling for assoc iation value or
meaningfulness , and mo re r ecently Underwood & Schulz
(1960) have s hown that pronunciablfltty is a lso an
importan t dete r minant of ea se of learning letter groups.

These mea sures, thou gh without doubt r eliable pre-
dictors, a re limited by the fact that norms a re required

before they ca n be u sed, that such norms a re only
available for ce r tain types of letter se quence (e. g.
CVCs , CCCs etc .), and that the norms a re based on
consensus of opin ion which need s to be laboriously
determined for each type of letter seque nce .
In 1958 Miller reported that ease of r ecall of
letter sequences was a function of lett er sequence
r edu ndancy thus including, probabl y, mo st of the ea rlier
measures in one whic h obviates the need for inde -
pend ently establi shed nor ms, and which ca n be applied
to any length of seque nce . Di Mascio (1959) r eported

that even single letter freque ncy was r el ated to memort-
zabiltty, and Underwood & Schulz (1960) reported

significant co r relations between ease of learning single
letters as r esponse te r ms in paired-associ ate learning,
and freque ncy of occurr ence in English. Baddel ey (1964)
showed that a simple -to-use ap proximation to second
or de r letter sequence r edundancy, which he ca ll ed
predictability, was a highly effe ctive predictor of
ease of learning, and since it was based on published

tables of digram fr equency (Badd el ey, Conrad & Thom-
so n , 1960) r equired no prior testing.

Badd el ey, Conrad & Hull (1965) measured the pre-
dictability of 40 6-conso nant seque nces and obtained a

highly significant cor relation with ease of shor t- te rm
memor izing. But when second-order effec ts we re

pa r tialled out , a Di Mascio (1959) single - le tter fr e-
quen cy mea su r e did not cor r elate signific antl y with

ease of memorizing.
Psvch on . Sci .. fi v nt . :1

Coming at verbal learning fro m an angle comple te ly
different fro m that ba sed on language habits of the kind
r eferred to, Conrad (1962, 1964) s howed that when
consonant sequences a re memorized for shor t- term
r ecall after visual presentation, memory er r ors cor -
r el ate highly with listeni ng er r ors in a conventional
intelligibility test for spoken consonants. This r esult
suggested that anothe r factor in determining the ease
with which a letter sequence could be learned, would
be the acous tic confu s ability of the letters within
the sequence. This predi ction was confi r med by Conrad
& Hull (1964) who in the same study showed that when
acous tic confusabil ity was held constant , infor ma tion in
the sequence was of mi nor impo rtance.
However, thes e measu r es of ac oustic confusabtlity
confounded predictability (letter-_sequence effects),
while the Baddel ey , Conr ad & Hull (1965) study of

predictability confounded effects of ac oustic con-
fusabihty. The presen t study was carr ied out in an

attempt to get ind ependent esti m ates of the effec ts
of these parameters.
ll.. lhod
Us ing all cons onants exce pt Z, 40 6- le tter se que nces
wer e r andomly gene rate d with the sole constraints that
no letter appeared mo re than once in a seque nce , and
letters occurred equally often in each se rial posi tion.

Seque nces were presented letter by lett er for immed-
iate r ecall by mean s of fr ame by frame film pr ojection

at a r ate of 80/min. Unlimited ti me for written r ecall
was allo wed . Ss were 45 paid housewives.
When the sequences had been gene rated to meet the
a bove cons traints, the probabil ity of ac qus ti c confus ion
was ca lcu late d for each sequence fro m the tabl e of
listening data given by Conrad (1964) . Similar ly the
predictabili ty for each sequence was ca lcula ted fro m
the tab le of digrams of the English language in

Badd eley, Conrad & Thom so n (1960). The rank cor rela-
tion between the two measures was .18 (p > .2).

B'-liuleN
The measur e of r ecall was simply the numb er of
letters in a sequence wrong for the particular seria l

pos ition . The mean numbe r of er r ors pe r subject /se-
quen ce was 1.5 1 (range: .54-3. 33). The er r or data were

fitted significantly well (F = 19.23, df: 2/ 37) by the
function: Y = .895 Xo + .059 Xl ' wher e Y =er ror s , Xo =
probability of acoustic confus ion, Xl =pr edi ctability .
The aco ustic simil ar ity component is significant at the
.001 level, the pr edictability component is s ignificant
at the .02 level.
Since lett er s occur r ed equr- pr oba bly in eac h se r ial

position, the total number of errors per letter was taken

as an index of ease of memorizing letters. The product-
moment correlation between frequency with which a

letter was wrongly recalled and frequency of listening
error (Conrad, 1964) was .75, p < .001. When language
fr equency was correlated with the "frequency with which
a letter was incorrectly given as response in the memory
task, the product-moment correlation was .09. When
language frequency was correlated with frequency of the
letter being wrongly recalled, the correlation was again
about .09.
Discussion
It se ems adequately shown that for short-term
storage of consonant sequences, encoding of presented
material depends much more on what the individual
letters sound lik e, than on the frequency with which
they have previously been met in the course of using
language. Single-letter frequency seems irrelevant to

the task and the results sharply qualify the SPEW hy-
pothesis of Underwood & Schulz (1960) which asserts

that the availability of verbal units as responses in
new associative connections depends on the frequency
with which they have previously been experienced.
However, when the index of experience is based on
higher order sequence relationships it does become
more important for memory. Nevertheless, Conrad
(1963) has shown that when letter sequence redundancy
is very high and relatively homogeneous, as with

common words, the acoustic properties ofthe word still
dominate. S's encoding strategy is probably dependent
on the time he has available for it.
References
Baddeley , A . D. Immediate memory and the " perception" of l etter
sequence s. Quart . J . expo Psu chol., 1964, 16, 364-367.

Badd eley , A . D., Conrad , R., & Hull, A . J . Predi ctab ility and i m-
mediate memory for consonant sequences. Quart. J . ex po Psuchol ..

1965 , 17 , 175-177 .
Badd eley, A . D. , Conrad , R., & Thomson , W. E . L ett er structure of
the En glish language. Nature , 1960, 186, 414-416 .
Conrad , R. An association between memory errors and errors due to
acoustic masking of speec h. Nature, 1962, 193, 1314-1315.
Conrad, R . Acoustic confusi ons and memory spa n for words. Nature,
1963, 197, 1029-1030.
Conrad , R. Acoustic confusions in i mmediate memory. Brit. J.
Psuch ot ., 1964, 55, 75-84.

Conrad , R., & Hull, A . J . Information, acoustic confusio n and mem-
ory span. Bri t . J . Psuchol., 1964, 55, 429-432.

Di Mascio, A . L earnin g characteristics of nonsense sy llables: A
fun ction of l etter fr equency. Psucliol, Rep. , 1959, 5, 585-591.
Miller, G. A . Free recall of redundant stri ngs of l etters. J . ex po
Psuchol ., 1958, 56, 485-491.
Underwood , B. J ., & Schulz , R. W. Meani ngf ul ness and ve rbal team -
i ng. New York: Lippin cott, 1960.
Note
1. This article was written whil e the senio r author (R . Conr ad) held
a positi on of Vi sitin g Sci entist at th e Human Perform ance Center,
Depart ment of P sy chol ogy, Univers ity of Mi chigan. Th i s post was
support ed by the Advanced Research Pro j ects Ag ency, Depart ment of



Topic/Research Title
Acoustic factors versus language factors in short-term memory
Name of author(s)
R Conrad, P R. Freeman and A J. Hull 
Publication date
1965
Name of the journal
Medical Research Council, Applied Psychology Research Unit, Cambridge, England



1.
Research Aim:
Understand the purpose of the study. What is the researcher trying to investigate?
An attempt to get independent estimates of the effects of acoustic confusability
2.
Hypothesis: 
Identify the hypothesis or predictions made by the researchers.
If acoustic confusability was held constant,then information in the sequence was of minor importance.
3.
Methodology




Participants: Note the sample size, demographics, and selection method.
45 paid housewives


Design: Understand whether the study is experimental, correlational, longitudinal, etc.
Correlational, as they were  trying to compare the estimates of the affects and would see if that if acoustic confusability was held constant, information was of minor importance


Procedures: Look at how the study was conducted, including any materials or tasks used.
Using all consonants except Z, 40 6-letter sequences were randomly generated with no letter appearing more than once in the sequence, letters occurring equally often in each serial position. Sequences were presented letter by letter for immediate recall, through frame by frame film projection at a rate of 80/min. They were able to have unlimited time for written recall. WHen the sequences were generated and met the above constraints, the probability of acoustic confusion was calculated for each sequence from the table of listening data.
4.
Results
Focus on the main findings. What data was collected, and what were the key outcomes?
Measure of recall was the number of letters in a sequence wrong for the particular serial position. 1.51
5.
Conclusion: 
Analyze the interpretations made by the researchers. Do they support the hypothesis?


6. 
Limitations: 
Consider any weaknesses or limitations of the study, such as sample bias or methodological flaws.
Relatively small sample size, only involved women, specifically those who are housewives instead of the general population. 
7. 
Ethical Considerations
Pay attention to how the study addressed ethical issues, such as consent and confidentiality.
None mentioned
8. 
Application: 
Think about how the findings can be applied in real-world contexts or relate to psychological theories.
These can be applied a lot into the Multi-store Model and working memory model, adding more insight, especially through how the brain processes and memorizes these information, through the sensory model, short-term memory and long-term memory.
9. 
Critical Evaluation:
Reflect on the study's strengths and weaknesses. How does it contribute to existing knowledge in psychology?


10.
Additional comments/notes (if any)
n/a




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