Ageing and development
Visual spatiotemporal processing in the elderly
Marina Kunchulia, Karin S. Pilz, Khatuna Parkosadze and Michael H. Herzog
We used backward masking paradigm to investigate the effects of aging on visual spatiotemporal processing. First, thirty-three older (M = 65.3 years) and ten younger adults (M = 24.3 years) had to indicate the offset direction of a vernier that was masked by a 5- or 25-element grating. We replicated results from our previous study (Roinishvili et al, 2011, Vision Research, 51(4):417-23) and found stronger masking effects in older compared to younger adults. Interestingly, stimulus onset asynchronies between target and mask were significantly longer in older adults whose individually determined vernier durations were above 30msec compared to older adults with vernier durations below or equal to 30msec. Second, we investigated effects of aging on visual spatiotemporal processing using two different masks with either a spatial or a temporal inhomogeneity. Older adults with vernier durations that were similar to young controls were sensitive to temporal and spatial inhomogeneities in the mask indicating fast and spatially intact processing. However, older adults whose individually determined vernier durations were significantly longer than those of younger adults were not as sensitive to temporal and spatial inhomogeneities in the mask, indicating that small spatio-temporal details are filtered out, which is highly likely due to blurred vision.
Changes of beta-band power reveal attentional deficits in visual performance of elderly subjects
Mateusz Gola, Mikolaj Magnuski, Izabela Szumska and Andrzej Wrobel
Older adults (65-85 years) show attentional deficits as compared to young (18-30 years) [Madden, 2007, Curr Dir Psychol Sci. 16: 70-74]. As increase of beta-band EEG activity was previously related to attentional modulation in the visual system [Wróbel, 2000, Acta Neurobiol Exp 60: 247-260], we searched for deficits in beta power in elderly subjects performing delayed attentional task with spatial differentiation between target visual stimuli. Two groups of older subjects were characterized by behavioral responses. High Performers did not differ from Younger subjects and showed increased beta activity in occipito-parietal cortex prior to proper behavioral responses. In contrast, Low Performers expressed lower activation in beta band during anticipatory period preceding appearance of target stimulus. In the second group performance and beta activity were significantly lower at the short (3-5 sec) and the longest (11 sec) periods of stimulus anticipation. We have thus confirmed that attentional deficits in a group of elderly subjects might result from lower activation in beta band at parieto-occipital cortex and that they correlate with disturbed mechanisms of alertness and sustained attention. In addition, we observed that the reduced level of behavioral performance is significantly related with decrease of gamma power in parieto-occipital cluster of EEG sources.
Early susceptibility to visual illusions after treatment for early-onset blindness
Pawan Sinha, Tapan Gandhi, Amy Kalia and Garga Chatterjee
The dominant account for many visual illusions is based on experience-driven development of sensitivity to certain visual cues. The Ponzo illusion, for instance, where two identical lines placed on a background of converging stripes appear to be of different lengths, is believed to arise from our learned association of 2D perspective cues with the distances they represent in the 3D world. While this explanation appears reasonable, it lacks direct experimental validation. To contrast it against an account that dispenses with the need for visual experience, we have to determine whether the susceptibility to the illusion is present immediately after birth. However, eliciting reliable responses from newborns is fraught with operational difficulties and studies with older infants are incapable of resolving this issue. Our work with children who gain sight after extended early-onset blindness (as part of Project Prakash) provides a potential way forward. We find that the newly sighted children, ranging in age from 8 through 17 years, exhibit susceptibility to several illusions (including Ponzo, Müller-Lyer and simultaneous brightness contrast) immediately after the onset of sight. This finding has implications not only for the likely explanations of these illusions, but more generally, for the nature-nurture argument as it relates to some key aspects of visual processing.
Consuming dietary flavonoids found in cocoa and berries improves performance on tests of visual function.
David T. Field, Michela Muggeo, Caroline Saunders, Claire Williams and Laurie Butler
There is a growing interest in the health benefits of a class of phytochemicals called flavonoids, found in particularly high concentrations in berry fruits and cocoa. Flavonoids are beneficial for the blood supply to the eye and the brain, have neuroprotective effects, and it has been suggested that they influence visual signal transduction in photoreceptors by accelerating rhodopsin regeneration. We therefore performed experiments to determine whether flavonoid supplementation improves performance on measures of visual system function, and have found improvements in the contrast sensitivity of young adults [Field et al., 2011, Physiology & Behavior, 103(3-4),255-260] as well as older adults. In young adults cognitive test performance also improved, but this was not the case for older adults. In the older adult study we measured acuity, and unlike contrast sensitivity this was not influenced by supplementation. Our most recent experiment detected effects of supplementation on accommodation of the lens and convergence of the eyes in young adults, and provided an indication that improved function at low light levels potentially underlies our earlier contrast sensitivity findings. Several hypotheses compete to explain these observations, including enhanced blood supply to the eye/retina, improved attention during tasks, and intervention of flavonoids in the rhodopsin cycle.
Effect of color and word cues on the following color discrimination task in the elderly
Satoko Ohtsuka, Masaru Takeichi and Takeharu Seno
We have recently reported that exposure to color and/or color-word cue interferes with later color discrimination task in young people (Ohtsuka & Seno, 2011). The interference was largest when the word was presented in conflicting color. In this study we examined the performance in the elderly. Old people, 60 years of age or more, were recruited as participants. In experimental trials they were asked to decide and respond as quickly and as accurately as possible whether the target was red or green. There were cue types of color, color word, congruent colored word, and conflict colored word besides a control. Cue duration was 150 msec with SOAs of 200 and 1,200 msec. As compared with the young people, the old generally responded slower as expected. The response was especially slower in the word cues irrespective of presentation color, unlike the young people showed it in the color cues. It appears that the elderly have greater difficulty in inhibiting word processing than color processing. Also the old participants'response was not promoted by the congruent cue. The elderly can be confounded by the multiplicity of information itself rather than the discrepancy among them.
The Rapid Peripheral Motion Contrast Threshold (RPMCT) Test : Preliminary Validation of a 2 Minute Screening Test for Older Driver Competency.
Heather Woods-Fry, Steven Henderson, Sylvain Gagnon and Charles A. Collin
Older drivers have an increased rate of automobile crashes per kilometer driven, likely due in part to age-related declines in motion perception. Our research group has developed the Peripheral Motion Contrast Threshold (PMCT) test as a measure of peripheral motion sensitivity. Results on this test correlate highly with indicators of driving performance in older individuals. However, the duration of the PMCT makes it impractical as a screening tool. Therefore, we developed the RPMCT task as a quicker alternative. Here, we compared the tests to determine if they yield similar results. Participants were 30 undergraduate students, assessed with both tasks. The PMCT presents participants with Gabors (0.4 cpd, 13.75°/s drift) at one of four locations 15° from fixation, and uses method of limits to measure contrast threshold. This takes approximately 10 minutes. RPMCT presents the same stimuli positioned 15° to either side of fixation, and uses a 2AFC variation on the Bekesy Method. It takes approximately 2 minutes. Results show a strong positive correlation between PMCT and RPMCT measurements, thus validating the quicker test. Ultimately, we aim to develop the RPMCT into part of a screening battery for distinguishing safe drivers from unsafe ones.
Does age impact on eye-movement patterns and perceptual biases during face processing?
Louise Williams and Stephen Butler
Using chimeric faces (where the left and right side differ on a specific dimension such as gender) it has consistently been found that perceptual and attentional biases are left lateralized. This is considered to reflect the right hemisphere's dominance in face processing. Theories of aging, however, predict that the right hemisphere becomes less dominant in older age (Park & Reuter-Lorenz, 2009, Annual Review of Psychology, 60, 173-196), thus reducing left lateral biases in older compared with younger adults. We used eye-tracking to quantify lateral bias differences between older (60+ years), and younger (18-30 years) adults in a chimeric gender judgment task. Our findings revealed that both groups displayed a left perceptual bias, basing most of their gender decisions on the left side; initial saccades were also leftward. Additionally, fixations were longer and more frequent when gender judgments were based on the left compared with the right side - but no between groups lateral bias differences were revealed. The response times of the older adults were, however, significantly slower than the younger group, potentially indicating underlying performance differences. As these results clearly contrast with accepted theories of aging, potential reasons for this and avenues for future research will be discussed.
Age-related differences in the perception of expressive movements in point-light displays of dancers
Ramona Kaiser, Vassilis Sevdalis and Peter E. Keller
An increasing amount of research investigates the perception of body movements by employing point-light displays. In a recent study, Sevdalis and Keller (2011, Psychological Research, 75: 423-434) demonstrated that observers are able to distinguish between expressive and inexpressive dance movements in such kinematic displays. Motivated by these findings, and by inconsistent effects of age on the perception of biological motion (see Troje, Faubert and Legault, 2012, i-Perception, 3, 104-111), we asked younger and older participants (N = 40; age-range: 20-60) to rate whether point-light videos of dance movements, performed with two musical pieces and tempi, represent an expressive or inexpressive dance style. All participants reported familiarity with the musical and dance styles that were presented. Younger and older participants were able to discriminate with greater than chance accuracy between the two different levels of expressivity in dance, although responses were - irrespective of age - biased towards 'expressive' ratings. Interestingly, younger adults showed significantly higher accuracy in detecting expressive intensity in dance compared to the older age group. Kinematic analyses are underway to investigate this age effect by examining which motion cues are meaningful for the discrimination ability of the younger and older participants.
A projection method for investigating indoor lighting needs of visually impaired people: validation
Frank Hoeben and Herman Talsma
Objectives: Optimisation of indoor lighting is an integral part of the rehabilitation of visually impaired people. A well illuminated environment is beneficial for making optimal use of residual vision capabilities. Visibility of the indoor environment can be improved by using general improvements like an optimal illumination level, creating illumination homogeneity, shielding off disturbing luminances and increasing useful contrasts. The range in which the illumination level is optimal and acceptable however, tends to be very dependent on the individual person. Cornelissen et al (1995) use a realistic test room (the LightLab) where the subject has to detect and recognize different every day objects under increasing illumination conditions. This test provides boundaries for an optimal illumination level and functions also as a way of experiencing the benefits of optimal lighting for a patient and his/her relatives. We adapted this test to make it more flexible for our purposes: · allowing for retesting by easier scene changing · availability of the test at more locations in our organization at limited cost · easier luminance control of specific objects within a scene · allowing for specific scenes for different groups, e.g adults, children and mentally disabled people We validated the new test for implementation in the rehabilitation practice. Methods: Investigated is the use of video projection with separate grey filters for precise luminance adjustment. Normal subjects were tested under increasing luminances. The normal subjects wore additional grey filter goggles. The stimuli consist of real life living room scenes. A validation of the projection (2D) lightlab is done by testing a group of visual impaired people both in the new setup and in the conventional (3D) LightLab Also the results are compared with clinical measurements such as visual acuity and contrast sensitivity. Results and conclusions: We report on technical comparison between 2D and 3D setup, and present preliminary test results of the validation setup. The results show that the 2D setup can be used for clinical measurements in the rehabilitation program of visually impaired people.
Ageing effects on visual field asymmetries within magno and parvocellular pathways
Maria Loureiro, Catarina Mateus, Bárbara Oliveiros, Pedro Fonseca and Miguel Castelo-Branco
Available evidence regarding anisotropies of nasal/temporal and superior/inferior retinal function have been previously documented based on anatomical and psychophysical measurements. We aimed to explore these asymmetries in normal ageing using contrast sensitivity (CS) tests that tackle magno- and parvocellular pathways. Monocular CS was measured using Frequency-Doubling Technology, a magnocellular biased test (FDT: 211 eyes; 34.76 ± 1.25 yrs, 10:83) and Intermediate Spatial Frequency perimetry (ISF: 191; 35.95 ± 1.26 yrs, 7:72). FDT stimuli were vertically sinusoidal gratings of 0.25 cycles per degree (cpd) undergoing 25 Hz counterphase flicker, and 3.5 cpd and 0 Hz for ISF. Temporal and/or superior patterns of disadvantage were found per age groups, using FDT: <20 yrs (T<N, p<0.001); [20;30[ (S<I, p=0.009); [30;40[ (T<N, p<0.001; S<I, p=0.025). For older age groups no patterns of asymmetry were found. ISF showed a pattern of nasal and/or superior disadvantage: <20, [20;30[ and [30;40[ (N<T, p=0.001); [40;50[ (N<T, p=0.03; S<I, p=0.002); [50,60[, n.s.; [60;[, S<I (p<0.001). The main finding was that different retinal based anisotropies occur across multiple visual pathways and are affected by ageing, especially for magno-biased perimetry (lost in older groups). Nasal/temporal asymmetry was opposite between magno- and parvocellular visual channels and both maintain a superior hemifield disadvantage.
Age-Related Changes of Contrast Discrimination Threshold and Contrast Response
Contrast sensitivity at threshold level declines with age. However, it remains unclear the quantitative age-related differences of contrast response arising from contrast stimuli. The reasons why those differences have not been clarified may be that contrast sensitivity depends on contrast intensity and it is difficult to directly compare contrast responses of different observers. Therefore, we conducted a contrast discrimination experiment using achromatic Gabor patches (3.24 x 3.24 degrees, average luminance: 47.5 cd/m2) with several kinds of spatial frequency (1, 2, 4, 8, 16 cpd) and contrast intensity C (0, 5, 10, 15, 20, 40, 60, 80 %) in young (23-27 yrs) and elderly (65-75 yrs) participants, and estimated contrast response functions from the data. In a trial, two Gabor patches with different contrast intensities C and C+dC were presented on a CRT-display and observers responded whether the two patches are the same or not. Experimental results show that contrast discrimination threshold depends on contrast intensity C and spatial frequency as well as age. We developed expressions for contrast sensitivity and contrast response as functions of age, spatial frequency and contrast intensity, and finally achieved to create simulated images seen by the elderly for young observers by using the calculated formulae.
Age-related changes in saccadic suppression
Senay Aydin, Velitchko Manahilov and Niall C. Strang
Saccades are rapid and frequent gaze shifts that scan visual environments and foveate objects of interest. Saccadic eye movements cause smearing and distort retinal images. However, these are not perceived due to saccadic suppression, which reduces visual sensitivity during saccadic onset. We investigated age-related changes in saccadic suppression of contrast sensitivity for discriminating the polarity (darker or brighter compared to the mean screen luminance) of a large horizontal bar (a half cycle of a cosine luminance profile with a width of 5 deg) during horizontal saccadic eye movements of 7 deg size. Young subjects (mean age 26±5.37 years, n=6) exhibited significant reduction of contrast sensitivity, compared to that without saccades, which started 50 ms before the saccadic onset, approached a maximum (220%) at the saccadic onset and lasted about 100 ms after the onset of the saccades. For older people (mean age 72.6±6.08 years, n=6), suppression of contrast sensitivity was only 25% during the saccadic onset and approached a maximum (116%) 50 ms after the onset of the saccadic eye movements. The reduced and delayed saccadic suppression in older adults suggest that they may perceive an unstable external world, which could affect their mobility in everyday environments.
On the relation between face perception and visuo-spatial abilities in normal and pathological aging
Delphine Gandini, Isabelle Rouleau and Sven Joubert
The aim of this study was twofold: (1) to examine the encoding strategies of face perception in healthy old individuals and patients with Alzheimer disease (AD), and (2) to determine the link between visuo-spatial abilities and face perception in these two populations. To do so, we tested two groups of participants, 20 healthy old subjects (mean age = 77.5 y.o) and 20 early-AD patients (mean age = 78.8 y.o), using a face matching task. To study encoding process of faces, we manipulated the inversion effect, referring to the findings that recognition of inverted faces is less accurate and more time-consuming than recognition of upright faces. In a first task, we compared perception of faces versus cars. In a second task, we manipulated distance between face attributes (e.g., eyes). Finally, the two groups were assessed with a series of visuo-spatial tests (e.g., Benton face, Benton line, VOSP). The results showed that healthy older participants and AD patients did not encode faces in the same way. Moreover, in AD patients, the mean percent errors on matching inverted faces negatively correlated with some measures of visuo-spatial abilities. These results have some implications for the understanding of the effect of AD on face perception.
Effect of age perception and lineup procedure on face recognition
Jae Seon Song, Woo Hyun Jung and Seungbok Lee
The purpose of this study is to test the effect of age perception on face recognition in simultaneous and sequential condition. Stimulus were pictures of Northern Asian female faces from the diverse age groups. For half of the cases, targets and distractors were from the same age group. For the rest, distractors were from diverse age groups. The results showed that participants recognized face more accurately in the sequential presentation condition. They also responded more accurately when both targets and distractors were from the different age groups. In addition, Also unlike to face perception, same age effect was not found. These results suggest that visual features for age perception are used for face recognition and memory. This work was supported by the National Research Foundation of Korea Grant funded by the Korean Government (NRF-2010-330-B00312)
Changing views: the role of ageing in the matching of unfamiliar faces across dynamic or static changes in viewpoint
Corrina Maguinness and Fiona N Newell
Previous reports, largely based on static images, have suggested that unfamiliar face recognition is worse in older than younger adults. However others report that recognition is best when faces are learned though dynamic rather than static presentations. Furthermore preserving the temporal order in which 'rigid'(e.g. rotation) face images are presented across viewpoints affects performance (Wallis and Bülthoff, 2001, PNAS, 98(8), 4800-4804). Here, we tested how the recognition of dynamic faces across changes in viewpoint is affected by the ageing process. Younger and older adults learned either a video, or a static sequence of discrete images of a face moving between a frontal and 45º view. Test images were either of a novel extrapolated or interpolated view (i.e. within the training set) of the face. We found that while face perception in younger adults benefited from multiple static image presentation, perception in older adults benefited from dynamic information during learning when the test face viewpoint was novel. Our results suggest that the integration of multiple static views into a single representation of a face becomes more difficult with ageing and that face perception in older adults may benefit from preserved temporal order of images, particularly when generalising across viewpoints. [Funded by The Innovation Academy, Trinity College Dublin]
Near-infrared spectroscopy detects specific inferior-frontal activation during visual memory tasks in elderly
The purpose of this study was to examine the hemodynamic response of the inferior-frontal area during recognition tasks using NIRS. A total of 15 young and 15 healthy old adults participated in the present study. Hemodynamic response in the prefrontal cortex was measured using a NIRS system. The recognition task were examined using digit stimuli, verbal sutimuli(visual stimuli that allow for verbal-name coding) and nonverbal sutimuli(visual stimuli that do not allow for verbal-name coding). During the digit and verbal recognition task, oxygenated hemoglobin concentrations increased and deoxygenated hemoglobin concentrations decreased in old adults. But it is observed different pattern in young adults.
Global motion perception at low speed is reduced due to increased internal noise and reduced sampling efficiency in young, mid-aged and old observers.
Lotte-Guri Bogfjellmo, Peter J. Bex and Helle Kristine Falkenberg
With age there is a reduction in motion perception, and the sensitivity is reduced for slow speeds. We have shown that the reduction in direction discrimination of global motion with age is due to both increased internal noise and reduced sampling efficiency. Using an EN paradigm, this study further explores how speed affects direction discrimination. 64 observers (16-19 years, 40-49 years, and 70-89 years) identified the direction of global motion in a 2AFC task. The 8 degree stimuli consisted of 100 moving band-pass dot elements with of 10% Michelsons contrast moving at 1.5 or 5.6 deg/s. Internal noise and sampling efficiency were estimated from the direction discrimination thresholds as a function of speed and age. Direction discrimination was significantly worse for 1.5 deg/s and in the oldest age group (p<0,05). The reduced sensitivity to slow motion in young and adults is mainly due to further increase in internal noise (p<0,05). For the oldest age group there is also a significant loss in sampling efficiency (p<0,05). The further reduction for speed indicates that speed is processed by two independent systems tuned to high and low speed, and that the channel for slow speed is more vulnerable to optical and neural age changes.
The effect of visual field loss on non-foveal visual localisation and pointing precision
Nikki Rubinstein, Andrew Anderson, Anna Ma-Wyatt, Mark Walland and Allison McKendrick
We investigated the effects of visual field loss on visual localisation judgements and the performance of visually guided hand movements. We tested 10 older adults (61-72 years) and 8 patients with glaucoma (55-76 years). Visual localisation and pointing precision were measured at four locations each at 15° eccentricity, with targets (0.5°, white dots, 174cd/m^2) presented on a black background (0.1cd/m^2). Testing was performed binocularly, to more closely resemble real world functioning and monocularly, to accentuate the effects of visual field loss. For the pointing task, experimental groups did not differ in pointing precision (p>0.05), with no effect of binocularity (p>0.05). Pointing precision was significantly reduced with reduced visual field sensitivity (F(1,132.0)=19.1, p<0.001, R^2=0.12). For the visual localisation task, monocular precision reduced with reduced visual field sensitivity (F(1,32.21)=11.37, p<0.01). Participants with glaucoma had reduced binocular visual localisation precision compared to controls (F(1,18.74)=4.66, p=0.04), but precision did not co-vary with visual field sensitivity (p>0.05). In summary, patients with visual field loss have reduced ability to locate objects both for perceptual judgements and visually guided actions. Perimetry provides only a small indication of the degree of this difficulty. Our data indicates that peripheral binocular function may be impaired in people with glaucoma.
The influence of auditory interference on imitations of observed sequential movements in young and older adults
John Stapleton and Fiona N. Newell
Recent studies have reported that visuo-spatial memory can be compromised in older adults. As a possible consequence, spatial navigation is more error prone in the older group, particularly under reduced visual conditions. Moreover, we reported that efficient perception in older adults depends more on multisensory than unisensory inputs. We investigated whether visual spatial memory can be enhanced by synchronous, or impaired by asynchronous, auditory cues in older persons. We adopted a reported task in which participants imitated observed linear movements using a stylus (Maryott and Sekuler, 2009, Psychology and Aging, 24(2), 476-486). We presented a sequence of 5 visual movements to younger and older participants who were subsequently asked to imitate this sequence on a touchscreen computer. An auditory cue occurred either congruently, or was temporally offset (pre- and post-visual stimulus), with the occurrence of a turn on the visual sequence. We found that older adults are more error prone than younger adults, as reported previously. Also, incongruent auditory cues differentially disrupted imitation performance in the older group. Our findings suggest age-related changes in multisensory influences on spatial memory.
A comparison of older and younger adult performance for multisensory integration of visual and auditory rate information
Allison Mckendrick, Cassandra Brooks, Andrew Anderson, Neil Roach and Paul McGraw
This experiment investigated interactions between visual and auditory rate perception in younger (aged 22-32, n = 10) and older (age 60-75, n = 6) adults. Observers were required to perform a rate discrimination task for each modality in isolation, and also when conflicting rate information was presented in the other sensory modality. Because auditory rate discrimination is typically more precise than visual rate discrimination, and because differences in low-level sensitivity may exist between older and younger adults in either the visual or auditory domains, rate discrimination performance was measured under conditions of equated auditory and visual sensitivity for each observer. For both groups, when the discrepancy between the visual and auditory rate was small, cues were partially integrated as has been shown previously (Roach et al, 2006, Proc R Soc B, 273: 2159-2168). Under conditions of equated unimodal sensitivity, the degree of cue integration did not differ between older and younger adults. This data suggests that normal aging does not impact on the flexible processes used by the brain to determine whether to integrate or segregate multisensory signals.
Spatial-frequency and category-specific deficits in normal aging
Pierre Bordaberry and Sandrine Delord
The objective was to investigate the deficit of spatial frequency (SF) with aging in a categorization task of object, and its relationship with a category-specific deficit. Thirty young and 24 mature adults had to categorize 120 photos of objects (animals/tools) presented for 200ms in one of three versions: normal, band-pass (1.9-6.7 cpd) and low-pass gaussian-filtered (0-3.8 cpd). Results showed three main effects: a global impairment in precision in the mature group, an overall SF-specific deficit (non-filtered > band-pass > low-pass) and a whole category-specific effect (animals>tools). Moreover, a SF-specific deficit effect with age was found, as the decreased precision for the mature group was restricted to band-pass filtered images. Furthermore, while there was no significant global category-specific effect with aging, the SF-specific deficit with aging interacted with category, as the decreased precision in the old group for the band-pass version was obtained for tools only. This interaction between the SF-specific deficit with aging and the category is discussed according to the relevant SF band for the task and to the structural similarity and dissimilarity of the items within the category. These variables could explain the discrepancy of previous results on category-specific effect in normal aging.
Words do not automatically activate semantic networks in the brains of already proficiently reading children
Tessa Dekker, Denis Mareschal, Martin I. Sereno and Mark H. Johnson
Prominent 'embodiment' theories argue that word meaning is represented in distributed cortical networks overlapping with sensory-motor regions. For example, words should activate the same brain regions as pictures of the objects they describe, and this co-activation should contribute to comprehension. We explored how a cortical category preference for written tool and animal names develops during the initial school-age years while children become proficient readers. Seven- to ten- year-old children and adults performed a one-back basic-level discrimination task with animal and tool pictures or their associated written words in an MRI scanner. Performance was consistent across age. All age groups showed clear differential cortical specialisation for tool and animal pictures. In adults, regions with a preference for tool or animal pictures, most notably the tool-specific left medial temporal gyrus and inferior frontal gyrus, showed similar activation patterns for tool and animal words. Thus, consistent with previous studies, object category representations were elicited merely by presenting the corresponding written word. In contrast, even older children who were proficient readers, showed no co-activation of picture-induced activation on the presentation of tool or animal words, suggesting that automatic activation of semantic tool and animal networks for words emerges after initial acquisition of word comprehension.
Do delay release the verbal overshadowing effect in child and adult eyewitnesses?
Valentine Vanootighem, Serge Brédart and Hedwige Dehon
The verbal overshadowing effect (VO) [e.g., Schooler and Engstler-Schooler, 1990, Cognitive Psychology, 22(1), 36-71] suggests that the fact of generating a verbal description of a previously seen face may impair subsequent performance on a lineup identification task in adults. Previous research has examined whether descriptions also impaired children's identification abilities but no evidence of VO was found [Memon and Rose, 2002, Psychology, Crime & Law, 8(3), 229-242]. However, the method might not have been appropriate to observe this effect as, for instance, a 24-hour delay between the description and the identification tasks (associated with a release of the VO effect in adults) was used. Hence, in this current experiment, groups of children (7-8, 10-11, 13-14 years old) and adults were presented with a short video and then assigned to a description or a no description condition before the identification task. Participants were also assigned either to a 'no delay', a '24-hour post encoding delay' or a '24-hour post description delay' condition to determine the influence of delay on the VO effect. Results indicated that, compared to the control condition, the description decreased correct identification performance in both children and adults and no release of VO was found with delay.
The development of speed discrimination abilities
Catherine Manning, David Aagten-Murphy and Liz Pellicano
The processing of speed is an important part of visual development, allowing children to track and interact with moving objects. Previous work has reported immature speed discrimination thresholds in 5-year-olds (Ahmed et al., 2005, Vision Research, 45, 2129-2135) but no study has investigated the developmental trajectory of speed discrimination abilities or precisely when these abilities become adult-like. Here, we measured speed discrimination thresholds in 5-, 7-, 9-, 11-year-olds and adults, using random dot stimuli with two different reference speeds (slow: 1.5 deg/sec; fast: 6 deg/sec). Sensitivity for both reference speeds improved exponentially with age and, at all ages, participants were more sensitive to the faster reference speed. However, sensitivity to slow speeds followed a more protracted developmental trajectory than that for faster speeds. Furthermore, sensitivity to the faster reference speed reached adult-like levels by 11 years, whereas sensitivity to the slow reference speed was not yet adult-like by this age. Different developmental trajectories may reflect distinct systems for processing fast and slow speeds (e.g., Edwards, Badcock & Smith, 1998, Vision Research, 38(11), 1573-1580). The reasonably late development of speed processing abilities may be due to inherent limits in the integration of neuronal responses in motion-sensitive areas in early childhood.
The Development of Global Motion Sensitivity in Children
Fleur Corbett and John Wattam-Bell
Global translational motion sensitivity matures around five years after global form sensitivity (Gunn et al., 2002, Neuroreport, 13, 843-847). The mechanism and development of global motion integration is not yet understood. This study investigated whether the extended maturation period is present in other motion types. Bertone and Faubert reported that sensitivity to global radial and rotational motion was reduced relative to global translational motion sensitivity (Bertone and Faubert, 2003, Vision Research, 43, 2591-2601). However, Blake and Aiba reported no significant differences between global translational, rotational or radial motion sensitivity (Blake and Aiba, 1998, Japanese Psychological Research, 40, 19-30). Form and motion sensitivity was measured in eighty-three 6-12 year olds with stimuli that required global spatial and temporal integration of signal elements. Participants had to detect coherent signal patches presented either side of a central fixation cross. Across the sample, form sensitivity was consistently higher than motion sensitivity. Sensitivity to rotational and radial motion was tightly coupled across the developmental trajectory and improved with age. However, sensitivity to translational motion was significantly poorer than radial or rotational motion sensitivity and did not correlate with age. This persistently low sensitivity to global translational motion suggests disparate developmental trajectories and requires further examination.
Coherent motion and coherent form perception in developmental dyslexia
Sara Giovagnoli, Sara Magri, Roberto Bolzani and Mariagrazia Benassi
The role of visual perception in Developmental Dyslexia (DD) is still controversial. Although the Magnocellular theory of DD has been widely criticized, it is still unclear if the deficit in motion perception is specific for the Magnocellular system or if it is connected to a general difficulty in discriminating signal to noise. The aim of this study is to investigate dorsal and ventral pathways in different conditions of noise in a population of DD. Seventeen DD and forty-three typically developed (TD) children (age 7-12 years) participated in the study. All the subjects performed the Motion coherence test and the Form coherence test. In the motion coherence test the ability in discriminating the direction of luminance coherent moving dots in different levels of noise is reported. The Form test measures the ability in form recognition in different condition of noise. The MANOVA showed that DD differed from TD both in the Motion and in the Form coherence tests. Moreover, these differences are significant only in intermediate noise conditions. These results are in accordance with the noise exclusion theory of DD and added important information about the DD deficit in discriminating signal to noise.
Developmental Processes in Audiovisual Object Recognition and Object Location
Maeve M Barrett and Fiona N Newell
This study investigated whether performance in recognising and locating target objects benefited from a cross-modal cue. We also examined developmental processes in these tasks by testing across different age groups. Using the same set of stimuli, participants conducted either an object recognition task (respond to two predefined animals out of four), or an object location task (respond to two predefined locations out of four). Target stimuli were presented either by vision alone, audition alone, or bimodally. Bimodal cues were either congruent or incongruent. Our results revealed that reaction time to target stimuli in both tasks benefited from the presence of a congruent cross-modal cue, relative to incongruent or unisensory conditions. In the younger adult group, the effect was strongest for response times although the same pattern was found for accuracy in the object location task but not for the recognition task. Following recent studies on multisensory integration in children (e.g. Brandwein, 2010; Gori, 2008), we then tested performance in children (i.e. 8-14 year olds) using the same task. Although overall performance was affected by age, our findings suggest interesting parallels in the benefit of congruent, cross-modal cues between children and adults, for both object recognition and location tasks.
Early development of dynamic shape perception on the slit viewing condition
Tomoko Imura and Nobu Shirai
Developmental processes of global shape and motion perceptions in infancy are relatively well described. For instance previous studies suggest that the sensitivity to global share develops relatively slower than that to global motion (c.f. Atkinson, 2000). In this study, we examined the ability to integrate both global information, motion and shape, in infancy. We adopted the slit viewing paradigm to investigate the ability to integrate spatio-temporal information in infants aged from three- to twelve-month-olds. An experimental session consisted of six familiarization trials and two test trials. Each infant was exposed to a line drawing of object moving back and forth behind a slit (0.7 or 1.2 deg in width) in familiarization trials, and was tested to a pair of line drawings in test trials. One of the two drawings in a test trial was a novel one, and the other was a drawing which previously appeared behind the slit in familiarization trials. The findings suggest that the infants aged 5-months and over looked longer at novel drawings than familiar ones in the test trials. This implies that the infants recognized whole shape of the line drawing under the slit viewing condition.