Landmark Task Research Articles

Dissociating perceptual and motor effects of prism adaptation in neglect

Prism adaptation reduces some symptoms of neglect; however the mechanisms underlying such changes are poorly understood. We suggest that prisms influence neglect by acting on dorsal stream circuits subserving visuomotor control, with little influence on perceptual aspects of neglect. We examined prism adaptation in three neglect patients and a group of healthy controls on line bisection and landmark tasks. Neglect patients showed a dramatic reduction in the rightward bias for line bisection, but absolutely no change in their leftward bias on the landmark task, which is a perceptual equivalent to bisection. However, in controls, prisms produced 'neglect-like' deficits on both the line bisection and landmark tasks. These data suggest that prisms influence visually guided actions more so than perception in neglect.

Prism adaptation influences perception but not attention: evidence from antisaccades

Prism adaptation has been shown to successfully alleviate symptoms of hemispatial neglect, yet the underlying mechanism is still poorly understood. In this study, the antisaccade task was used to measure the effects of prism adaptation on spatial attention in healthy participants. Results indicated that prism adaptation did not influence the saccade latencies or antisaccade errors, both strong measures of attentional deployment, despite a successful prism adaptation procedure. In contrast to visual attention, prism adaptation evoked a perceptual bias in visual space as measured by the landmark task. We conclude that prism adaptation has a differential influence on visual attention and visual perception in healthy participants as measured by the tasks used.

The geometry of the Landmark Task.

In the Landmark Task participants are shown a horizontal line divided into two segments by a transection mark (“landmark”), and asked to compare the lengths of the two segments [3,4]. This comparison can in principle be carried out by (i) considering the stimulus as a single object and assessing whether or not it is left-right symmetrical [1], or (ii) interpreting the two segments as separate objects, mentally translating one over the other and deciding whether they are congruent (see also [2,5,6]). When stimulus lines are rectangles, which is typically the case, the two types of process cannot be easily distinguished because symmetrical stimuli are (by definition) formed by two congruent segments and non-symmetrical stimuli are formed by non-congruent segments. The purpose of this work is to separate out the contribution of symmetry processing from that of translation-congruencyprocessing by using trapezoidal instead of rectangular shapes.

The geometry of the Landmark Task

The geometry of the Landmark Task

Clements-Cortes, A. (2009). Episodes of relationship completion through song: Case studies of music therapy research in palliative care. VDM Verlag, 356 pages, ISBN 978-3-639-14542-7. $106.00

Clements-Cortes, A. (2009). Episodes of relationship completion through song: Case studies of music therapy research in palliative care. VDM Verlag, 356 pages, ISBN 978-3-639-14542-7. $106.00Canadian music therapist Amy Clements-Cortes offers the reader engaging and beautiful narratives of case studies in palliative care based on the model of relationship completion as outlined by Dileo & Dneaster (2005). This model includes three levels of practice: supportive (palliative endof-life symptoms like pain, comfort, quality of life); communicative/expressive (i.e., launching and reflective techniques, musical autobiographies, improvisation); transformative (i.e., life review, resolve conflicts and feelings, address spiritual issues). Through the detailed presentation and deconstruction of four poignant case studies (the accompanying CD, Episodes of Relationship Completion, can be purchased through her website, notesbyamy.com), one can readily see the effectiveness of music therapy facilitated relationship completion. The author believes that relationship completion is part of holistic care of the dying. Clements-Cortes describes songwriting, lyric discussion and analysis, life review and the creation of musical gifts as beneficial techniques for assisting persons with relationship completion at end of life. Anchoring her approach in Dileo & Dneaster's model gives the music therapist a tool to address end-of-life opportunities for relationship completion.Relationships in this study involve any relationship that the dying person has a desire to complete that is of an intrapersonal (with oneself), interpersonal (with other people), and/or transpersonal nature (with God, pets, nature etc.) (pp. 22-27) The literature shows that relationship, whether intrapersonal, interpersonal or transpersonal, are highly valued in terminally ill people. According to Byock, there are 1 0 tasks for the end-of-life. He defines them as:...sense of completion with worldly affairs, sense of completion in relationships with the community; sense of meaning about one's individual life; experienced love of self; experienced love of others; sense of completion in relationships with family and friends; acceptance of the finality of life and of one's existence as an individual; sense of a new self beyond personal loss; sense of meaning about life in general; and surrender to the transcendent and the unknown (p. 3).Understanding how music therapy can assist in relationship completion, one of these landmark tasks, is the central inquiry of the book. According to Byock, there are five sentiments that permit relationship to reach completion once they are expressed. These are:I love you, Thank you, Forgive me, I forgive you, and Goodbye (p. 15).A secondary question in the book is how music therapists introduce the concept of relationship completion to clients. Clements-Cortes believes that the techniques employed in receptive, creative, re-creative, and combined approaches of music therapy are useful with respect to relationship completion in potentially three ways: a) to bring focus or clear thinking to set the work of relationship completion in motion b) to serve as launching points or reflections about relationships, and/or c) to become vehicles or tools for expression of the various sentiments that permit relationships to close. …

Hormone exposure and functional lateralisation: Examining the contributions of prenatal and later life hormonal exposure

An increasing amount of research has shown a relationship between hormonal exposure and functional lateralisation. In this study different sources of hormonal exposure were examined: prenatal exposure, estimated using the 2D:4D ratio, and later life exposure through examining the effects of hormone replacement therapy. In addition to considering multiple sources of hormonal exposure, three tests of functional lateralisation were used: two versions of the chimeric faces test, one using positive emotion and the other using negative emotion, and the landmark task. The same effects were found across all three measures of lateralisation. Lower 2D:4D ratios, which indicate high levels of prenatal testosterone exposure, were associated with stronger right hemisphere dominance. Later life hormonal exposure was not found to be associated with any of the lateralisation measures. This finding suggests a relationship between prenatal hormonal exposure and brain organisation.

Effects of Psychostimulants on Alertness and Spatial Bias in Healthy Participants

Converging evidence from neuropsychological and neuroimaging studies suggests that the ability to maintain an alert, ready-to-respond state is mediated by a network of right-hemisphere frontal and parietal cortical areas. This right lateralization may help to explain why visuospatial hemineglect, a cluster of deficits in detecting and responding to contralesional stimuli, is more common and persistent after right-hemisphere lesions. Indeed, it has been hypothesized that this asymmetry reflects a direct, functional link between alertness and spatial attention. In the present study, we investigated whether a pharmacologically induced increase in alertness would influence lateral bias in healthy people. Eighteen healthy participants were each given placebo or the psychostimulant drugs methylphenidate 40 mg or modafinil 400 mg on separate days and completed an hour-long version of the spatially sensitive landmark task. For those participants who demonstrated the expected alerting effect of modafinil, there was a significant Condition by Time interaction, consistent with the effects of the drug resisting time-on-task rightward drifts in spatial bias in the placebo condition. In contrast, no effect of methylphenidate on spatial bias was observed. These results suggest that spatial bias may be modulated by a psychostimulant-induced increase in alertness, supporting the hypothesis of a direct, functional link between right-hemisphere systems controlling alertness and visuospatial attention.

Brain activity during landmark and line bisection tasks

Neglect patients bisect lines far rightward of center whereas normal subjects typically bisect lines with a slight leftward bias supporting a right hemisphere bias for attention allocation. We used fMRI to assess the brain regions related to this function in normals, using two complementary tasks. In the Landmark task subjects were required to judge whether or not a presented line was bisected correctly. During the line bisection task, subjects moved a cursor and indicated when it reached the center of the line. The conjunction of BOLD activity for both tasks showed right lateralized intra-parietal sulcus and lateral peristriate cortex activity. The results provide evidence that predominantly right hemisphere lateralized processes are engaged in normal subjects during tasks that are failed in patients with unilateral neglect and highlight the importance of a right fronto-parietal network in attention allocation.

Spatial Attentional Bias as a Marker of Genetic Risk, Symptom Severity, and Stimulant Response in ADHD

Attention-deficit hyperactivity disorder (ADHD) is a heritable childhood onset disorder that is marked by variability at multiple levels including clinical presentation, cognitive profile, and response to stimulant medications. It has been suggested that this variability may reflect etiological differences, particularly, at the level of underlying genetics. This study examined whether an attentional phenotype-spatial attentional bias could serve as a marker of symptom severity, genetic risk, and stimulant response in ADHD. A total of 96 children and adolescents with ADHD were assessed on the Landmark Task, which is a sensitive measure of spatial attentional bias. All children were genotyped for polymorphisms (3' untranslated (UTR) and intron 8 variable number of tandem repeats (VNTRs)) of the dopamine transporter gene (DAT1). Spatial attentional bias correlated with ADHD symptom levels and varied according to DAT1 genotype. Children who were homozygous for the 10-repeat allele of the DAT1 3'-UTR VNTR displayed a rightward attentional bias and had higher symptom levels compared to those with the low-risk genotype. A total of 26 of these children who were medication naive performed the Landmark Task at baseline and then again after 6 weeks of stimulant medication. Left-sided inattention (rightward bias) at baseline was associated with an enhanced response to stimulants at 6 weeks. Moreover, changes in spatial bias with stimulant medications, varied as a function of DAT1 genotype. This study suggests an attentional phenotype that relates to symptom severity and genetic risk for ADHD, and may have utility in predicting stimulant response in ADHD.

Timing of visuo-spatial information processing: Electrical source imaging related to line bisection judgements

This study deconvolves the temporal dynamics of the neural processes underlying line bisection judgements (i.e., the landmark task). Event-related potentials (ERPs) were recorded from 96 scalp electrodes in 10 healthy right-handed male subjects while they were judging whether horizontal lines were correctly prebisected. In the control task, subjects judged whether or not the horizontal line was transected by a vertical line, irrespective of its position. Using a current density reconstruction approach, source maxima in the time range from 50 to 400ms after stimulus onset were localized and the time courses of activation were elaborated. Five regions, corresponding to those revealed by our previous fMRI studies (e.g., [Fink, G. R., Marshall, J. C., Shah, N. J., Weiss, P. H., Halligan, P. W., Grosse-Ruyken, et al. (2000). Line bisection judgments implicate right parietal cortex and cerebellum as assessed by fMRI. Neurology, 54, 1324–1331]), were identified as contributing significant source activity related to line bisection judgements: right middle occipital gyrus (Brodmann area; BA18); bilateral inferior occipital gyrus (BA19); right superior posterior parietal cortex (BA7) and right inferior posterior parietal cortex (BA40). Temporal deconvolution indicated sequential activation of these regions starting at BA18 as early as 90ms post-stimulus onset, followed by the successive activation of the right superior posterior parietal (BA7), bilateral inferior occipital (BA19) and right inferior posterior parietal cortex (BA40). Three of these areas (BA18, BA17 and BA19) became reactivated within 250ms of stimulus onset.The data provide evidence for an early involvement of the right hemispheric parietal network in visuo-spatial information processing. Furthermore, the temporal deconvolution of the electrophysiological data suggest that iterative processes between and within parietal (dorsal path) and occipital areas (ventral path) mediate bisection judgements.

Acetyl‐L‐carnitine and α‐lipoic acid supplementation of aged beagle dogs improves learning in two landmark discrimination tests

Beagle dogs between 7.6 and 8.8 years of age administered a twice daily supplement of alpha-lipoic acid (LA) and acetyl-L-carnitine (ALC) over approximately 2 months made significantly fewer errors in reaching the learning criterion on two landmark discrimination tasks compared to controls administered a methylcellulose placebo. Testing started after a 5 day wash-in. The dogs were also tested on a variable delay version of a previously acquired spatial memory task; results were not significant. The improved performance on the landmark task of dogs supplemented with LA + ALC provides evidence of the effectiveness of this supplement in improving discrimination and allocentric spatial learning. We suggest that long-term maintenance on LA and ALC may be effective in attenuating age-associated cognitive decline by slowing the rate of mitochondrial decay and cellular aging.

The middle house or the middle floor: Bisecting horizontal and vertical mental number lines in neglect

This study explores the processing of mental number lines and physical lines in five patients with left unilateral neglect. Three tasks were used: mental number bisection (‘report the middle number between two numbers’), physical line bisection (‘mark the middle of a line’), and a landmark task (‘is the mark on the line to the left/right or higher/lower than the middle of the line?’). We manipulated the number line orientation purely by task instruction: neglect patients were told that the number-pairs represented either houses on a street (horizontal condition) or floors in a building (vertical condition). We also manipulated physical line orientation for comparison. All five neglect patients showed a rightward bias for horizontally oriented physical and number lines (e.g. saying ‘five’ is the middle house number between ‘two’ and ‘six’). Only three of these patients also showed an upward bias for vertically oriented number lines. The remaining two patients did not show any bias in processing vertical lines. Our results suggest that: (1) horizontal and vertical neglect can associate or dissociate among different patients; (2) bisecting number lines operates on internal horizontal and vertical representations possibly analogous to horizontal and vertical physical lines; (3) at least partially independent mechanisms may be involved in processing horizontal and vertical number lines.

Time-on-task effect in pseudoneglect

Neurologically normal subjects systematically misbisect space during visual line-bisection or similar tasks, generally erring to the left of the veridical center when bisecting horizontal lines, a phenomenon referred to as pseudoneglect. This phenomenon is usually interpreted as enhanced attention toward the left hemispace resulting in an overestimation of the leftward extent of a line. While most studies have examined the role of attention in spatial bias using spatial cueing methods in bisection tasks, Manly et al. (Neuropsychologia 43(12):1721-1728, 2005) proposed an original paradigm in which the participants' alertness was diminished by sleep deprivation or prolonged execution of a line-bisection task. The authors reported a significant rightward shift in attention related to declining alertness, but they did not control eye movements and, consequently, modifications of scanning and fixation strategies with fatigue cannot be ruled out in their study. Here we examine whether a diminution in alertness induced by a 60-min-long Landmark task would diminish (or even reverse) this attentional bias, when eye movements are absent. Participants performed a forced-choice judgment about the location of a transaction mark in relation to the veridical center of a horizontal line. The results confirmed a significant decrease in the leftward bias over the course of the session but, in contrast to the findings of Manly et al. (2005), we did not observe a reverse bias from the left to the right hemispace. The results are discussed within the context of the hemisphere-activation model.

Impaired visual search in drivers with Parkinson's disease

To assess the ability for visual search and recognition of roadside targets and safety errors during a landmark and traffic sign identification task in drivers with Parkinson's disease (PD). Seventy-nine drivers with PD and 151 neurologically normal older adults underwent a battery of visual, cognitive, and motor tests. The drivers were asked to report sightings of specific landmarks and traffic signs along a four-lane commercial strip during an experimental drive in an instrumented vehicle. The drivers with PD identified significantly fewer landmarks and traffic signs, and they committed more at-fault safety errors during the task than control subjects, even after adjusting for baseline errors. Within the PD group, the most important predictors of landmark and traffic sign identification rate were performances on Useful Field of View (visual speed of processing and attention) and Complex Figure Test-Copy (visuospatial abilities). Trail Making Test (B-A), a measure of cognitive flexibility independent of motor function, was the only independent predictor of at-fault safety errors in drivers with PD. The cognitive and visual deficits associated with PD resulted in impaired visual search while driving, and the increased cognitive load during this task worsened their driving safety.

The Neural Mechanisms Underlying the Müller-Lyer Illusion And Its Interaction with Visuospatial Judgments

Arrows terminating a line can distort the perceived line length. This so-called Müller-Lyer illusion can be used in healthy human subjects to mimic the performance of neglect patients in visuospatial judgments (e.g., in the landmark task). In this study, we investigated the neural mechanisms underlying the Müller-Lyer illusion, the landmark task, and their interaction. This was achieved by parametrically manipulating the magnitude of the Müller-Lyer illusion both in a landmark and in a luminance (control) task. As expected, the landmark task activated right posterior parietal cortex and right temporo-occipital cortex. In contrast, the neural processes associated with the strength of the Müller-Lyer illusion were located bilaterally in the lateral occipital cortex as well as the right superior parietal cortex. The data not only converge with but also extend neuropsychological data that indicate maintained line-length illusion in neglect patients. In addition, our results support the size-constancy scaling hypothesis as a putative mechanism underlying line-length illusions. Furthermore, activation that was driven by both the task and the strength of the Müller-Lyer illusion was observed in right intraparietal sulcus, thus arguing in favor of an interaction of illusory information with the top-down processes underlying visuospatial judgments in right parietal cortex.

Do Parietal Cortical Lesions Impair Spatial Attention or Allocentric Spatial Perception?

It remains unclear whether monkeys with large parietal cortical lesions fail “landmark” tasks because they cannot judge the relative distances between landmark and response locations, or because they fail to attend to, or even to notice, the landmark. Monkeys with small posterior parietal (SPP), large posterior parietal (LPP), superior temporal sulcus (STS), or frontal eye field (FEF) lesions were tested on a landmark task in which the physical salience of the landmark and its location varied. Only the LPP monkeys were impaired, seemingly because they overtly failed to shift attention during each trial, responding to whichever food well they looked at first. A task based on one used with neurological patients was therefore introduced in which the monkeys had to discriminate between two white square plaques each containing a spot, where the spot on the positive stimulus was centrally placed. Solving this task requires an allocentric judgement about the relative location of each spot to the edges of the plaque. Even on the most difficult discrimination, monkeys with large parietal lobe lesions were unimpaired. The deficits previously reported on landmark tasks probably reflect a failure of spatial attention or attention to objects rather than an inability to judge allocentric spatial relationships.

Dominance for language and spatial processing: limited capacity of a single hemisphere

Using functional magnetic resonance imaging during word generation and spatial judgement (Landmark task), we investigated how hemispheric specializations for language and spatial processing interact in healthy individuals. We found individuals with atypical, right-hemispheric dominance for language to have more bilateral activation during spatial judgement than individuals with typical, disjunct hemispheric specialization, that is, left dominance for language and right dominance for spatial tasks. These findings suggest that hemispheric specializations for language and spatial functions interfere to some extent and favour additional recruitment of the opposite hemispheres for spatial functions.

Driver landmark and traffic sign identification in early Alzheimer’s disease

Objective: To assess visual search and recognition of roadside targets and safety errors during a landmark and traffic sign identification task in drivers with Alzheimer’s disease. Methods: 33 drivers with...

Driver Identification of Landmarks and Traffic Signs after a Stroke

A study was done to assess the ability for visual search and recognition of roadside targets and safety errors during a landmark and traffic sign identification task in drivers with stroke, that is, drivers who have had a stroke. Visual search for roadside targets during automobile driving can compete for a driver's cognitive resources and may impair driving, especially in drivers with cognitive impairment caused by stroke. Thirty-two drivers with stroke and 137 neurologically normal older adults underwent a battery of visual, cognitive, and motor tests and were asked to report sightings of specific landmarks and traffic signs along a segment of an experimental drive. The drivers with stroke identified significantly fewer landmarks and traffic signs and showed a tendency to make more at-fault safety errors during the task than did control subjects. Roadside target identification performance and safety errors were predicted by scores on standardized tests of visual, cognitive, and motor function. Drivers with stroke are impaired in a task of visual search and recognition of roadside targets whose demands on visual perception, attention, executive functions, and memory probably increased the cognitive load and worsened their driving safety.

Driver Identification of Landmarks and Traffic Signs After a Stroke

A study was done to assess the ability for visual search and recognition of roadside targets and safety errors during a landmark and traffic sign identification task in drivers with stroke, that is, drivers who have had a stroke. Visual search for roadside targets during automobile driving can compete for a driver's cognitive resources and may impair driving, especially in drivers with cognitive impairment caused by stroke. Thirty-two drivers with stroke and 137 neurologically normal older adults underwent a battery of visual, cognitive, and motor tests and were asked to report sightings of specific landmarks and traffic signs along a segment of an experimental drive. The drivers with stroke identified significantly fewer landmarks and traffic signs and showed a tendency to make more at-fault safety errors during the task than did control subjects. Roadside target identification performance and safety errors were predicted by scores on standardized tests of visual, cognitive, and motor function. Drivers w...