Aging and Temporal Patterns of Inhibition of Return
Linda K. Langley,1Luis J. Fuentes,2Ana B. Vivas,3and Alyson L. Saville1
1Department of Psychology and Center for Visual Neuroscience, North Dakota State University, Fargo.
2Departamento de Psicologı ´a Ba ´sica y Metodologı ´a, Universidad de Murcia, Spain.
3Department of Psychology, City Liberal Studies, Affiliated Institution of the University of Sheffield,
Inhibition of return (IOR), an inhibitory component of spatial attention that is thought to bias visual search
toward novel locations, is considered relatively well preserved with normal aging. We conducted two experiments
to assess age-related changes in the temporal pattern of IOR. Inhibitory effects, which were strongly reflected in
the performance of both younger adults (ages 18–34 years) and older adults (ages 60–79 years), diminished over
a period of 5 s. The time point at which IOR began to diminish was delayed by approximately 1 s for older adults
compared with younger adults; this pattern was observed on both a target detection task (Experiment 1) and
a color discrimination task (Experiment 2). The finding that timing characteristics of IOR are altered by normal
aging has potential implications for the manner in which inhibition aids search performance.
understand the cognitive mechanisms that underlie this ability.
For example, how is it that searched locations are mentally
tagged so as to prevent unnecessary reexamination? Posner and
Cohen (1984) proposed that inhibition plays an important role
in this tagging function. In the context of a spatial orienting
study, they observed that a peripheral visual event (e.g.,
brightening of one of two boxes) was followed by a facilitated
processing of items presented at that location, presumably as
a result of a reflexive shift of attention toward the event. This
facilitation occurred if the target item appeared within 300 ms
of the orienting event. However, if attention was shifted either
extrinsically by a visual event occurring elsewhere (e.g.,
brightening of a central cue) or intrinsically by a long time
interval that brought attention back to fixation, an inhibitory
aftereffect could be measured in terms of a delayed responding
to items subsequently presented at the initial location. Posner
and Cohen thought that this inhibition of return (IOR) effect
functioned to bias attention toward novel locations, and Klein
(1988) later proposed that IOR served to discourage reinspec-
tions during visual search, thus increasing search efficiency.
Consistent with a search interpretation, subsequent studies have
provided evidence that observers do indeed use inhibition when
navigating complex search scenes (Klein, 1988; Klein &
MacInnes, 1999; Kristjansson, 2000).
Reduced inhibitory control may account, at least in part, for
age-related changes in search performance. Older adults are
generally slower and more distractible than young adults during
visual search, particularly on inefficient tasks that require
effortful, sequential search through the display (Foster,
Behrmann, & Stuss, 1995; Humphrey & Kramer, 1997; Plude &
Doussard-Roosevelt, 1989). Although there is evidence that
sensory changes and generalized cognitive slowing contribute
to changes in search (Madden, 2001; Scialfa, 1990), attention-
specific factors such as inhibition also likely contribute to it.
Consistent with this idea, recent studies have found age-related
changes in the time course of IOR (Castel, Chasteen, Scialfa, &
Pratt, 2003; Langley, Fuentes, Hochhalter, Brandt, & Overmier,
EOPLE rely on spatial attention to locate goal-relevant
items in the visual environment, and it is important to
2001). In the following sections, we review findings relevant to
the timing characteristics of IOR and age differences in these
Time Course of IOR
How quickly does IOR develop at a location, and how long
does it last? In a recent graphical meta-analysis, Samuel and
Kat (2003) addressed these questions by plotting IOR scores as
a function of cue–target stimulus onset asynchrony (SOA) for
studies that used a single peripheral cue (i.e., there was no
central cue to extrinsically redirect attention toward fixation).
Inhibited rather than facilitated orienting responses to the cued
location were reliably observed as early as 300 ms and were
maintained as long as 1,500 ms. However, there were few data
points beyond 1,500 ms; follow-up experiments indicated that
inhibitory effects lasted somewhere between 2 and 3 s.
Other research has found that although inhibition can remain
at a particular location for as long as 5 s (Berlucchi, Chelazzi, &
Tassinari, 2000; Danziger, Kingstone, & Snyder, 1998), the
magnitude of IOR declines with increasing cue–target interval
(Berlucchi et al.; Klein, 2000; Riggio, Bello, & Umilta, 1998).
This temporal decline would be optimal for aiding search
performance if inhibition were a limited resource; inhibition
would be strongest for the most recently searched locations, and
inhibition would diminish for earlier searched locations to free
up resources for newly inspected sites. Studies using multiple
cues have found just such a pattern; IOR could be maintained at
multiple locations, but inhibition diminished in magnitude for
earlier cued locations (Dodd, Castel, & Pratt, 2003; Snyder &
Kingstone, 2000). Support for the idea that inhibition is
resource limited can also be found in studies that report re-
duced negative priming (a nonspatial form of distractor inhi-
bition) under resource-demanding conditions (Engle, Conway,
Tuholski, & Shisler, 1995; Neumann & DeSchepper, 1992).
Tasks Demands and Timing of IOR
Inhibitory effects are robust on IOR tasks that require the
simple detection of objects, but initial studies to examine IOR
on tasks that require discrimination of target features
Journal of Gerontology: PSYCHOLOGICAL SCIENCES
2007, Vol. 62B, No. 2, P71–P77
Copyright 2007 by The Gerontological Society of America
(e.g., indicate the color or orientation of a target) failed to find
IOR (Tanaka & Shimojo, 1996; Terry, Valdes, & Neill, 1994).
Later studies demonstrated inhibitory effects for discrimi-
nation tasks when longer cue–target intervals were assessed,
revealing that IOR developed later on discrimination tasks
(e.g., 700 ms) than on detection tasks (e.g., 400 ms; Lupia ´n ˜ez,
Milan, Tornay, Madrid, & Tudela, 1997; Lupia ´n ˜ez & Milliken,
1999; Lupia ´n ˜ez, Milliken, Solano, Weaver, & Tipper, 2001).
Explanations for time course differences in IOR as a function of
task demands have focused on the interplay of facilitation and
inhibition initiated by the peripheral cue. For example, Klein
(2000) argued that the development of inhibition is delayed on
discrimination tasks because discrimination requires a higher
attentional control setting than detection (because of the greater
difficulty with perceptual discrimination of the target). This
higher setting remains relatively fixed throughout task perfor-
mance and thus influences processing of the cue as well as the
target. Heightened attention increases dwell time on the cue,
enhancing early facilitation effects. With delayed disengage-
ment of attention from the cue, it takes longer for facilitation
effects of the cue to diminish and inhibition toward the cued
location to be revealed, as compared with performance under
lower control settings such as with simpler detection tasks (see
Lupia ´n ˜ez et al., 2001 for a similar explanation).
Aging and Temporal Patterns of IOR
Among studies that have examined age differences in the
temporal patterns of IOR, in their study, Castel and colleagues
(2003) found that the time point at which IOR first develops is
delayed with age. On a single-cue IOR task, the cue–target
SOA at which facilitated responses turned to inhibition was 222
ms for younger adults and 592 ms for older adults. Similar to
the detection–discrimination explanation already described, the
interpretation offered by Castel and colleagues was that the age-
related delay in inhibition was due to task difficulty. Because
older adults found the detection task more difficult than
younger adults did, they allocated more attention for a longer
duration to cued locations, delaying the onset of IOR.
Most research described to this point has used a single-cue
IOR task. Another widely used IOR paradigm is the cue-back
task, in which a second central cue reflexively draws attention
back to fixation. The advantage of this task is that the timing of
the observable shift from facilitation to inhibition in perfor-
mance is less variable because the cue-back manipulation
encourages extrinsic rather than intrinsic disengagement of
attention from the initial cue. As a result of greater control over
the development of IOR, stronger emphasis can be placed on
manipulating and measuring the duration and resolution of
The predominant pattern across aging studies that have used
the cue-back task is a modest reduction in IOR at longer cue–
target intervals, with a similar pattern of decline for younger
and older adults (Experiment 2, Faust & Balota, 1997;
Experiments 1 and 4, Hartley & Kieley, 1995). However, it is
important to note that these studies used a restricted range of
temporal intervals, with the longest SOA being 1,800 ms
(Experiment 2, Faust & Balota). In a recent study (Langley
et al., 2001), we included a cue–target interval that was
sufficiently long (3,500-ms SOA) to demonstrate the resolution
of IOR for younger adults. Both younger and older adults
demonstrated IOR effects at the short cue–target interval (950-
ms SOA). However, whereas younger adults showed a signif-
icant decline in IOR (from 42 ms to 11 ms) as the temporal
interval increased, older adults showed a small increase in IOR
(from 25 ms to 33 ms). This pattern of results suggests that the
resolution of IOR is delayed or altered with age.
The Present Study
Our purpose in the present study was to further explore age
differences in the temporal maintenance and resolution of IOR.
We were interested in (a) the time point at which IOR begins to
diminish for younger and older adults, (b) how long IOR is
maintained in each age group, and (c) whether age differences
in the IOR time course varied with task demands. To this end,
we assessed IOR on a cue-back task at four cue–target intervals
(SOAs of 950, 2,200, 3,450, and 4,700 ms). We chose these
intervals because they would be sufficiently long to observe
dissipation and resolution of IOR effects. Participants completed
a detection task in Experiment 1 and a color discrimination task
in Experiment 2.
We based our predictions for age and task differences in the
time course on an attentional control setting theory (Klein,
2000) as applied to a cue-back task. We reasoned that control
settings influence processing of the second central cue as well
as the initial peripheral cue. The central cue serves to disengage
attention from the cued location, which encourages inhibition
rather than facilitation of attention at that location. Higher
control settings may enhance facilitation effects of the
peripheral cue, but this facilitation will be tempered by
extrinsic reorienting toward the central cue. When attention
returns to the central fixation, higher control settings will
enhance engagement of the central cue. We hypothesized that
this increased engagement at fixation would intensify inhibition
at the initially cued location, which would be reflected in longer
maintenance of IOR.
Because older adults would perceive both the detection and
discrimination tasks to be more difficult than younger adults
would, we predicted that older adults would have higher
attentional control settings than younger adults. As a result,
IOR would be maintained longer for older adults than younger
adults, and this pattern would generalize to both the detection
and discrimination tasks. Pertaining to task difficulty, both
younger and older adults would have higher control settings for
the more difficult discrimination task, so IOR would be
maintained more strongly on the discrimination task than on
the detection task.
Participants were 32 younger adults (19 women, 13 men) and
32 older adults (21 women, 11 men). Screening and
demographic data are provided in Table 1. Younger adults, in
the age range of 18–32 years, were students in psychology
courses at North Dakota State University who received extra
credit for participating. Older adults, in the age range of 61–79
years, were residents from the Fargo–Moorhead community
LANGLEY ET AL.
who received $20. All participants had at least a high school
education. According to self-reports on a health screening
questionnaire (Christensen, Moye, Armson, & Kern, 1992), all
participants were free of medical conditions that could impair
cognitive functioning (e.g., heart disease, stroke, neurological
diseases such as Parkinson’s or Alzheimer’s disease, drug or
alcohol abuse). Corrected near visual acuity was 20/40 or better
as assessed with a Snellen eye chart (Precision Vision, La Salle,
IL), and color vision was normal (9 points or higher out of 11)
as assessed with Ishahara color plates (Kanehara Trading Inc.,
Tokyo, Japan). All participants scored 9 points or lower on the
Geriatric Depression Scale (Yesavage & Brink, 1983), in-
dicating minimal depressive symptomatology, and 26 points or
higher on the Mini-Mental State Examination (Folstein,
Folstein, & McHugh, 1975), indicating no observable signs
of dementia or cognitive impairment. We excluded an
additional 12 participants (4 younger adults and 8 older adults)
from the data analysis for failing to meet the aforementioned
Materials and Stimuli
Stimuli were displayed on a 17-in. (43.18 cm) color monitor
controlled by a personal computer with a Pentium 4 processor.
Responses were made on a Model 200A five-button PST Serial
Response Box (Psychology Software Tools, Pittsburgh, PA),
and a chin rest maintained the participant’s viewing distance at
We created the experimental task by using E-Prime, Version
1.1 (Psychology Software Tools). We had stimuli presented
against a black background in three white unfilled boxes
arranged vertically in the center of the screen. The boxes
subtended visual angles of 2.28 in width by 2.98 in height, and
the centers were separated by 4.78. Target stimuli consisted of
red and green Xs, shown in Arial font, subtending visual angles
of 1.08 squared.
With two levels of cue–target relation (cued and uncued) and
four levels of cue–target interval (SOAs of 950, 2,200, 3,450,
and 4,700 ms), there were eight conditions. There were 24 trials
per condition, which resulted in 192 cue–target trials. The
inclusion of 48 catch trials (20% of trials), in which a cue was
presented without an accompanying target, led to a total of 240
test trials. We divided trials into three blocks of 80 test trials (64
target trials and 16 catch trials). Each block consisted of two
iterations of the 32 unique trials produced from all possible
combinations of cue location (top–bottom), target location
(top–bottom), target color (red–green), and cue–target interval
(950, 2,200, 3,450, and 4,700 ms). Similarly, the 16 catch trials
per block contained 8 trials for each of the top and bottom cue
The session lasted approximately 1 hr for younger
participants and 1.5 hr for older participants. The experimenter
explained the task to participants by using verbal instructions
and a drawn representation of stimulus events. Test trials were
preceded by 20 practice trials. The trial sequence, as outlined in
Figure 1, began with a fixation cross presented for 500 ms that
was replaced by three white boxes that stayed on the screen for
the remainder of the trial. After 1,000 ms, the top or bottom box
filled to white for 300 ms, serving as the initial spatial cue. The
boxes reverted to white outline and black fill for 200 ms before
the center box filled to white for 300 ms (the central cue). An
interval corresponding to a cue–target SOA of 950, 2,200,
3,450, or 4,700 ms was presented before the target stimulus
appeared at either the location of the initial cue (the cued
condition) or the other peripheral box (the uncued condition).
The target remained on the screen until the participant
responded or 10 s had elapsed. On catch trials, we interposed
an SOA of 6,800 ms before the fixation display of the next trial.
The experimenter instructed participants to press the center
Table 1. Participant Characteristics for Experiments 1 and 2
Exp. 1: Detection Exp. 2: Discrimination
M SDM SD
YA OAYAOA YA OAYAOA
Notes: YA ¼ younger adult group; OA ¼ older adult group; SD ¼ standard
deviation. WASI ¼ Wechsler Abbreviated Scale of Intelligence (Wechsler,
1999); the maximum score on the vocabulary subscale is 80 points, with
a higher score indicating better performance. Snellen acuity ¼ denominator of
the Snellen fraction (20/ __) for corrected near vision; a smaller number indi-
cates better vision. Color vision was assessed with the Ishahara color plates;
the maximum score is 11, with a higher score indicating better color vision.
MMSE ¼ Mini-Mental State Examination; the maximum score is 30 points,
with a higher score indicating better performance. GDS ¼ Geriatric Depres-
sion Scale; the maximum score is 30, with a higher score indicating more de-
pressive symptoms. An asterisk indicates that mean scores differed between
age groups according to an independent t test, p , .05.
Figure 1. Sequence of events for a sample trial in Experiments 1
and 2. Stimuli are not scaled to size. In the experiment, white outlined
boxes were presented against a black background, and the target ‘‘X’’
was printed in red or green. In Experiment 1 (detection trials),
participants pressed a single button as soon as they detected the target.
In Experiment 2 (discrimination trials), participants pressed one of two
buttons to indicate the color of the target.
AGE AND INHIBITION OF RETURN TIME COURSE
button of the response box with the index finger of their
dominant hand as soon as they detected the target. Speed was
emphasized but not at the expense of accuracy. The
experimenter told the participants to keep their gaze focused
on the center box for the duration of the trial. No information
was provided on the validity of the cue.
We removed two types of outliers: reaction time (RT) values
that were less than 150 ms or more than 2,000 ms, and RTs that
differed from an individual participant’s cell mean (for each
combination of task condition) by more than 2.5 SD. This
approach eliminated 3.0% of trials for younger adults and 2.3%
of trials for older adults. Table 2 displays the mean RTs for
A 2 34 32 mixed analysis of variance (ANOVA) with age
group (younger adults and older adults) as the between-subjects
factor and cue–target SOA (950, 2,200, 3,450, and 4,700 ms)
and target location (cued and uncued) as the within-subjects
factors revealed all main effects to be significant: age group,
F(1, 62)¼17.19, p , .0001, gp2¼.22; SOA, F(3, 186)¼5.28,
p , .01, gp2¼.08; and target location, F(1, 62)¼109.09, p ,
.0001, gp2¼.64. Older adults were slower than younger adults
(453 vs 392 ms, respectively), and RTs at the 4,700-ms SOA
(430 ms) were significantly slower than those at the 2,200-ms
SOA (416 ms). The IOR effect (Figure 2) was evidenced by
slower responses in the cued condition than in the uncued
condition (430 vs 415 ms, respectively). In addition to main
effects, there were significant two-way interactions of SOA 3
Location, F(3, 186)¼7.44, p , .0001, gp2¼.11, and Group3
Location, F(1, 62) ¼ 15.20, p , .001, gp2¼ .20, reflecting
modulation of IOR effects. The three-way Group 3 SOA 3
Location interaction was not significant, p . .40.
To examine the two-way interactions, we calculated IOR
effects for each participant by subtracting uncued RTs from
cued RTs. [To address the possibility that age differences in
IOR effects were due in part to generalized slowing, we also
computed individuals’ IOR effects as a percentage of their
uncued RT by using this formula: (cued RT ? uncued RT)/
uncued RT3100. The statistical significance patterns, for both
Experiments 1 and 2, did not differ as a function of the type of
IOR change score.] As assessed by Bonferroni-corrected t tests,
the SOA 3 Location interaction was due to IOR effects that
were significantly greater at the 950-ms SOA (24 ms) than at
the 3,450-ms or 4,700-ms SOAs (8 ms and 10 ms, re-
spectively). The Group 3 Location interaction was due to
significantly greater IOR effects for older adults (20 ms) than
for younger adults (9 ms). One-way ANOVAs conducted at
each SOA revealed that the only cue–target interval for which
age differences in IOR were significant was the 2,200-ms SOA,
F(1, 62) ¼ 12.23, p , .001, gp2¼ .21.
As a final analysis, we examined the time point at which IOR
effects resolved. Older adults’ IOR effects were significantly
greater than zero (as measured by individual t tests) at all four
SOAs, ts . 3.0, ps , .01. Younger adults’ IOR effects were
significantly greater than zero at the two shortest SOAs (950 ms
and 2,200 ms), ts . 3.0, ps , .01, but not at the two longest
SOAs (3,450 ms and 4,700 ms), ts , 2.0, ps . .05.
Error rates are presented in Table 2. Anticipation responses
(responding before the target was presented) and response
failures (failing to respond after the target was presented) were
rare (less than 1% for each age group). Thus, we conducted no
Table 2. Mean RTs and Error Rates as a Function of Age Group,
SOA, and Target Location for Experiments 1 and 2
Exp. 1: DetectionExp. 2: Discrimination
RT Ms (ms)
Error Ms (%)
Notes: RT ¼ reaction time; SOA ¼ stimulus onset asynchrony between the
initial cue and target; YA ¼ younger adults; OA ¼ older adults; C ¼ cued loca-
tion; U ¼ uncued location; SD ¼ standard deviation. An asterisk indicates that
the mean cued RT varied significantly from the uncued RT by t test, p , .05.
Figure 2. Mean inhibition of return (IOR) scores (6 1 SE) as a
function of age group and cue–target SOA for the target detection task
of Experiment 1. The IOR score is equal to the cued reaction time (or
RT) minus the uncued RT. An asterisk indicates a significant differ-
ence between age groups in IOR score as indicated by t test, p , .05.
LANGLEY ET AL.
The two main findings of Experiment 1 were these: first,
IOR effects diminished with increasing cue–target delay;
second, IOR effects were greater for older adults than for
younger adults. As we predicted, these findings together
suggest that resolution of IOR was delayed with age. In fact,
IOR effects had resolved between 2 and 3 s for younger adults
but could still be observed in the performance of older adults
at 4.5 s. In addition, age differences in IOR magnitude were
most apparent at 2 s (2,200-ms SOA), a time point at which
IOR had begun to diminish for younger but not older adults.
Overall, the results of Experiment 1 suggest that timing is an
aspect of IOR that changes with age.
In Experiment 1, we found the predicted age-related delay
in the resolution of IOR on a target detection task. Our
purpose in Experiment 2 was to determine if this age effect
would be replicated or even exaggerated on a color discrim-
ination task, in which task difficulty (and presumably the
attentional control setting) is increased. We used the same IOR
trial sequence as in Experiment 1, but now we asked
participants to make a two-choice color discrimination
response. We predicted that the diminishment of IOR effects
would be delayed compared with that observed in Experiment
1, as a result of the increased task difficulty (and thus, higher
attentional control settings) of a color discrimination task as
compared with a target detection task. We also predicted that
older adults would again demonstrate a slower-resolving
pattern of IOR than younger adults, and this age difference
may be accentuated on this task as compared with the
detection task because of increased age differences in
perceived task difficulty (and thus greater discrepancies in
attentional control settings).
Participants were 28 younger adults (12 men, 16 women;
ages 18–34 years) and 28 older adults (8 men, 20 women; ages
60–79 years); demographic and screening data are reported in
Table 1. None of the participants had taken part in Experiment
1. We excluded an additional 9 participants (1 younger adult
and 8 older adults) for failing to meet inclusion criteria.
Materials and Procedure
The materials, stimuli, and procedures were identical to those
described in Experiment 1, except that the experimenter
instructed participants to press one of two buttons to indicate
the color of the target (red or green). We counterbalanced
button assignment across participants.
Removal of RT outliers (RT , 150 ms, RT . 2,000 ms, or
RT . 2.5 SD from the condition mean) eliminated 2.7% of
trials for younger adults and 3.0% of trials for older adults.
Mean RTs for correct trials are presented in Table 2.
A 2 3 4 3 2 mixed ANOVA revealed all main effects to be
significant: age group, F(1, 54) ¼ 15.59, p , .001, gp2¼ .22;
cue–target SOA, F(3, 162)¼19.19, p , .0001, gp2¼ .26; and
target location, F(1, 54) ¼ 26.08, p , .0001, gp2¼ .33. Older
adults were slower than younger adults (783 and 589 ms,
respectively), and RTs increased as SOA did (669, 678, 688,
and 708 ms for SOAs of 950, 2,200, 3,450, and 4,700 ms,
respectively). The IOR effect was evidenced by slower
responses to targets at the cued location compared with the
uncued location (693 vs 679 ms, respectively).
In addition to main effects, there was a significant two-way
SOA 3 Location interaction, F(3, 162) ¼ 4.62, p , .01, gp2¼
.08, which was qualified by a three-way Age 3 SOA 3
Location interaction, F(3, 162) ¼ 2.78, p , .05, gp2¼ .05. To
examine the three-way interaction, we again calculated IOR
effects by using difference scores (Figure 3). For older adults,
IOR effects at 2,200 ms and 3,450 ms were significantly greater
than IOR effects at 4,700 ms, F(3, 81) ¼ 3.69, p , .05, gp2¼
.12. For younger adults, IOR effects at 2,200 ms were
significantly greater than IOR effects at 3,450 ms, F(3, 81) ¼
3.72, p , .05, gp2¼ .12. One-way ANOVAs at each SOA
revealed significant age differences in IOR at 3,450 ms,
F(1, 54) ¼ 6.86, p , .05, gp2¼ .11, with greater IOR effects
for older adults, but not at the other three SOAs.
As measured by individual t tests, older adults’ IOR scores
were significantly greater than zero at the three shortest SOAs,
ts . 2.4, ps , .05, but younger adults’ IOR scores were
significantly greater than zero only at the two shorter SOAs,
ts . 2.8, ps , .01.
Figure 3. Mean inhibition of return (IOR) scores (6 1 SE) as
a function of age group and cue–target SOA for the color
discrimination task of Experiment 2. The IOR score is equal to the
cued reaction time (or RT) minus the uncued RT. An asterisk indicates
a significant difference between age groups in IOR score as indicated
by t test, p , .05.
AGE AND INHIBITION OF RETURN TIME COURSE
Error rates are presented in Table 2. Combining the various
types of errors (anticipation responses, failures to respond, and
incorrect responses), we found that error rates were less than
3% for each age group; therefore, we did not conduct further
Both younger and older adults demonstrated robust in-
hibitory effects on the color discrimination task, with
diminishing IOR as cue–target interval increased. Replicating
Experiment 1, we found that there were age differences in the
temporal pattern of IOR. Whereas IOR effects began to
diminish after 2,200 ms for younger adults, no such decline
began until after 3,450 ms for older adults, resulting in an age-
related increase in IOR at 3.5 s postcue. Thus, in both
experiments, older adults maintained inhibition approximately
1 s longer than did younger adults. The findings differ from
those of Experiment 1 in the time point at which IOR began to
decline; reductions in IOR for both age groups began
approximately 1 s later on the discrimination task (Experiment
2) than on the detection task (Experiment 1). There was no clear
evidence that the age difference in the timing of IOR was
accentuated on the discrimination task as compared with the
If inhibition is a limited resource (Engle et al., 1995),
a desirable temporal profile for IOR would be one in which
inhibition develops quickly for a searched location and then
dissipates gradually to make resources available for sub-
sequently searched locations. The results of Experiments 1 and
2 were consistent with this pattern; IOR effects were robust at
early cue–target intervals and then diminished over a course of
5 s. As predicted, the time point at which IOR began to decline
was delayed by age, and this pattern was observed on both
a detection and a discrimination task. This age-related change
in the resolution of IOR was consistent with past findings
(Langley et al., 2001) and complimented single-cue findings of
age differences in the development of IOR (Castel et al., 2003).
This study revealed age differences in spatial-based inhibition
that might not have been observed on an IOR task measured at
a single temporal interval. In fact, inhibitory effects at the
shortest cue–target interval (950 ms), an interval at which IOR
effects are commonly examined, did not vary by age on either
that inhibition remained at a particular location. With a cue-back
task we were able to observe age differences in the maintenance
of IOR, whereas research with a single-cue task has revealed age
differences in the development of IOR (Castel et al., 2003).
Together,theresults callinto questionthe conclusionthat spatial
variants of inhibition are relatively unaffected by age, and the
findings could have important implications for how effectively
inhibition aids older adults’ search performance in cluttered
visual displays. On the one hand, slower-developing and longer-
lasting inhibition may be beneficial to older adults. With age-
related slowing in search rates, older adults search fewer
locations in a particular period of time, and delayed diminish-
mentin IORreduces the chancesof prematurereturn ofattention
locations can be simultaneously inhibited. If this is the case, then
the effectiveness with which inhibition contributes to the search
performance of older adults could be compromised by delayed
timing. Thus, although this study revealed age differences in the
resolution of IOR, it is for future studies to determine whether
this difference represents an adaptive change to accommodate
older adults’ slower search rates or a sign of decline in the
effectiveness with which inhibition assists search.
With regard to task difficulty, we predicted enhanced
inhibitory effects on the discrimination task as compared with
the detection task. To more directly evaluate support for this
prediction, we compared task differences in IOR patterns across
the two experiments; the results are reported in Table 3. For
younger adults, IOR effects had resolved by 3,450 ms on both
tasks, but the magnitude of IOR was significantly greater on the
discrimination task than on the detection task at 2,200 ms. For
older adults, there was a nonsignificant trend for IOR effects to
be greater for discrimination than detection at 3,450 ms (p ¼
.13), but contrary to predictions, IOR was greater on the
detection task than the discrimination task at the longest SOA
(4,700 ms). Thus, there was mixed support for enhanced IOR
effects on the discrimination task. Although IOR on the
discrimination task maintained its magnitude longer (particu-
larly for younger adults), it was resolved just as quickly, if not
more quickly, than IOR on the detection task. However, this
pattern must be interpreted cautiously, as data from separate
experiments were compared.
Consistent with Klein (2000), we argue that attentional
control settings moderated the observed influence of age and
task demands on temporal patterns of inhibition. Control
settings were adjusted on the basis of the perceived demands of
the task; older adults perceived both detection and discrimina-
tion tasks to be more difficult than did younger adults, and both
age groups perceived discrimination tasks to be more difficult
than detection tasks. With a cue-back task, we hypothesized
that a higher control setting enhanced processing of the central
Table 3. IOR Effects as a Function of Task and SOA for
Younger and Older Adults
Younger Adults Older Adults
SOA (ms)DetectDiscrim. DetectDiscrim.
IOR Ms (ms)
Notes: Inhibition of return (IOR) effects ¼ cued reaction time minus
uncued reaction time; SOA ¼ stimulus onset asynchrony between the initial
cue and target; Detect ¼ detection task (Experiment 1); Discrim. ¼ discrimina-
tion task (Experiment 2); SD ¼ standard deviation. An asterisk indicates that
the magnitude of IOR effects varied significantly between tasks as indicated
by t test, p , .05.
LANGLEY ET AL.
cue, leading to stronger inhibitory orienting toward the initially Download full-text
cued location. The finding that IOR maintained its peak
magnitude longer (a) for older adults compared with younger
adults and (b) for discrimination tasks compared with detection
tasks supports a control settings interpretation. The finding of
age-related temporal delays in IOR on both the detection and
discrimination tasks suggests that age and task demands
uniquely contributed to attentional control settings.
This research was conducted at North Dakota State University and was
supported by Grant 01322899 from the National Science Foundation, Grant
P20 RR020151 from the National Center for Research Resources of the
National Institutes of Health, and Grant SEJ2005-01223/PSIC from the
Ministerio de Educacio ´n y Ciencia of Spain.
We are grateful to Atiana Stark, Tomi Hanson, Sara Kveno, Scot
Dewitz, Jaryn Allen, Brandon Dosch, David Hughes, Jessica Ihry, Nichole
Keller, Laura Klubben, Savannah Kraft, Shelly Manger, Marie Schaaf, and
Melissa Tarasenko for assistance with data collection.
Address correspondence to Linda K. Langley, Department of Psychol-
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Received October 13, 2005
Accepted July 25, 2006
Decision Editor: Thomas M. Hess, PhD
AGE AND INHIBITION OF RETURN TIME COURSE