Carolina Murd - Academia.edu (original) (raw)

Papers by Carolina Murd

Article published in NeuroReport, 28(2), 111-114. (2017)

Vision research, Jan 1, 2010

Strong visual masking originates from sensory perceptual interactions between target and mask and... more Strong visual masking originates from sensory perceptual interactions between target and mask and also from attentional competition between target and mask even though mask does not correspond to attentional control settings. The relative contributions of these different masking mechanisms are difficult to estimate. One strategy to begin approach this problem is to use the same stimulus as a mask and as a non-informative singleton in a selective attention task. The purpose of the present study was to find the spatial and temporal intervals where a strong object mask interferes with target-object search when used as a non-informative singleton. In visual search for target location, we found that a visual object that has a strong forward and backward masking power on target-object correct perception when spatially superimposed on target can impair target perception from a spatially separated location only when presented up to 100 ms after the target and only from a spatially close location. These results are explained by a processing account where the initial analysis of stimuli features allows to determine the best candidate location for the target, but as soon as this location is established, a nearby later appearing object may intrude it, replacing the target in explicit perception. The higher-level mechanisms based interpretation is strengthened by the finding that any local masking effects of the same adjacent singleton were absent in the task of single-target identification.

Neuropsychologia, Jan 21, 2015

Dopaminergic system of the brain is believed to be strongly involved in normal and pathological b... more Dopaminergic system of the brain is believed to be strongly involved in normal and pathological behavioral phenotypes of attention. In metacontrast masking studies attentional effects on metacontrast are predominantly expressed when time intervals between a target stimulus and a masking stimulus are longer rather than shorter. Taken together, this predicts that variability in common genes known to be involved in dopaminergic function could interact with target/mask intervals in determining the effects of metacontrast masking. We tested this by genotyping participants of the masking experiment for the COMT Val158Met, DAT1 3'UTR 40bp VNTR, and DRD4 exon 3 48bp VNTR variability. We found that Val homozygotes and subjects with long repeat variants of the DRD4 gene showed relatively higher level of correct target perception with a longer target/mask time interval than with a shorter time interval while DAT1 variability did not have any effects. Implications of this result for the dev...

Frontiers in Human Neuroscience, 2014

In our previous study we found that it takes less time to detect coloration change in a moving ob... more In our previous study we found that it takes less time to detect coloration change in a moving object compared to coloration change in a stationary one (Kreegipuu etal., 2006). Here, we replicated the experiment, but in addition to reaction times (RTs) we measured visual evoked potentials (VEPs), to see whether this effect of motion is revealed at the cortical level of information processing. We asked our subjects to detect changes in coloration of stationary (0(°)/s) and moving bars (4.4 and 17.6(°)/s). Psychophysical results replicate the findings from the previous study showing decreased RTs to coloration changes with increase of velocity of the color changing stimulus. The effect of velocity on VEPs was opposite to the one found on RTs. Except for component N1, the amplitudes of VEPs elicited by the coloration change of faster moving objects were reduced than those elicited by the coloration change of slower moving or stationary objects. The only significant effect of velocity on latency of peaks was found for P2 in frontal region. The results are discussed in the light of change-to-change interval and the two methods reflecting different processing mechanisms.

Vision Research, 2012

Causal relevance of the cortical area V5/MT for motion (aftereffect) perception has been shown wh... more Causal relevance of the cortical area V5/MT for motion (aftereffect) perception has been shown when rTMS pulses have been applied onto this area, leading to disruption of the percept. Typically, the inducing and test stimuli have consisted in a spatially contiguous area from where stimulation is presented. Observers have had no need to divide attention between spatially remote areas including motion-related signals with different vectors. Here we present experimental results showing that an adverse effect of rTMS on motion aftereffect can be obtained when contralateral V5/MT is stimulated and subjects have to report which one of the two simultaneous aftereffect percepts separated into two hemifields decays before the other. The effect appears stronger following right hemisphere V5/MT stimulation and is clearly evident even with weak rTMS pulses.

Vision Research, 2006

The colour-changing stimulus paradigm is based on a tacit assumption that kinematic attributes (v... more The colour-changing stimulus paradigm is based on a tacit assumption that kinematic attributes (velocity, movement direction) do not aVect the detection of colour change . In this study three experiments are reported that clearly demonstrate that the time needed to detect changes in colouration of a moving stimulus becomes shorter with its velocity. The reduction of reaction time with increase of velocity is a purely kinematic eVect independent on the reduction of reaction time caused by the stimulus uncertainty eVects. It is concluded that colour coding mechanisms are not totally ignorant about movement parameters. 

Vision Research, 2010

Previous research has reported that attention to color afterimages speeds up their decay. However... more Previous research has reported that attention to color afterimages speeds up their decay. However, the inducing stimuli in these studies have been overlapping, thereby implying that they involved overlapping receptive fields of the responsible neurons. As a result it is difficult to interpret the effect of focusing attention on a phenomenally projected target-afterimage. Here, we present a method free from these shortcomings. In searching for a target-afterimage patch among spatially separate alternatives the target fades from awareness before its competitors. This offers a good means to study neural correlates of visual awareness unconfounded with attention and enabling a temporally extended pure phenomenal experience free from simultaneous inflow of sensory transients.

Vision Research, 2011

In searching for the target-afterimage patch among spatially separate alternatives of color-after... more In searching for the target-afterimage patch among spatially separate alternatives of color-afterimages the target fades from awareness before its competitors . Covert spatial attention in search for the location of a color-afterimage patch speeds up its decay from awareness: Introducing a method useful for the study of neural correlates of visual awareness. Vision Research 50, 1048-1053). In an analogous study presented here we show that a similar effect is obtained when a target spatial location specified according to the direction of motion aftereffect within it is searched by covert topdown attention. The adverse effect of selective attention on the duration of awareness of sensory qualiae known earlier to be present for color and periodic spatial contrast is extended also to sensory channels carrying motion information.

Swiss Journal of Psychology, 2013

Scandinavian Journal of Psychology, 2011

Visual metacontrast masking may depend on the time intervals between target and mask in two quali... more Visual metacontrast masking may depend on the time intervals between target and mask in two qualitatively different ways: in type-A masking the smaller the mask delay from target the stronger the masking while in type-B masking maximal masking effect is obtained with a larger temporal delay of the mask. Variability in the qualitative apperance of masking functions has been explained by variability in stimuli parameters and tasks. Recent research on metacontrast masking has surprisingly shown that both of these types of functions can be found with an identical range of stimulation parameters depending on individual differences between observers. Here we show that obtaining clear-cut type-A masking depends on whether target and mask shapes are congruent or incongruent and whether observers use the cues available due to the congruence factor. Conspicuously expressed type-A masking is selectively associated with incongruent target-mask pairings. In the latter conditions target identification level significantly drops with the shortest target-to-mask delays.

Psychological Research, 2012

One fundamental property of the perceptual and cognitive systems is their capacity for prediction... more One fundamental property of the perceptual and cognitive systems is their capacity for prediction in the dynamic environment; the flash-lag effect has been considered as a particularly suggestive example of this capacity (Nijhawan in nature 370:256-257, 1994, Behav brain sci 31:179-239, 2008). Thus, because of involvement of the mechanisms of extrapolation and visual prediction, the moving object is perceived ahead of the simultaneously flashed static object objectively aligned with the moving one. In the present study we introduce a new method and report experimental results inconsistent with at least some versions of the prediction/extrapolation theory. We show that a stimulus moving in the opposite direction to the reference stimulus by approaching it before the flash does not diminish the flash-lag effect, but rather augments it. In addition, alternative theories (in)capable of explaining this paradoxical result are discussed.

Perception, 2009

The time needed to detect changes in the colouration of a single moving stimulus becomes shorter ... more The time needed to detect changes in the colouration of a single moving stimulus becomes shorter with its increasing velocity (Kreegipuu et al, 2006 Vision Research 46 1848-1855). We examined the ability to detect colour change in moving chromatic bars or sinusoidal gratings through temporal order judgment (TOJ) and reaction time (RT) tasks to test whether the effect of velocity found in a previous study is universal and holds for different tasks and stimuli. The results demonstrate that the TOJ and simple RT to the colour change of a moving grating are insensitive to stimulus velocity. Therefore, we conclude that the process of comparison of the two internal representations of external events does not have access to temporal information precise enough to estimate the exact time when something enters our subjective awareness. The motion effect on colour-change perception seems to be confined to a single stimulus that moves across the visual field, to events that contain some spatial predictability, and to tasks that reflect the time of the change relatively directly.

Brain Research Bulletin, 2010

State dependent effects on brain processes are difficult to study due to the task-related confoun... more State dependent effects on brain processes are difficult to study due to the task-related confounds. Even in simple task environments external stimuli inevitably interact with dynamically changing states of the brain. Psychopharmacological manipulation and transcranial magnetic stimulation can be used independently of variations in subject's experimental task and environmental stimulation. Our aim was to show the investigative potential of combining these two methods for studying the effects of the state of the brain on the dynamics of task-free evoked brain activity. Caffeine was used for inducing higher arousal state and transcranial magnetic stimulation was used to evoke widespread bioelectrical responses of the brain. Occipitally delivered magnetic pulses caused increased global negativity of the brain potentials, but no speed-up of brain potentials when caffeine was administered. The relative negativization effect was most clearly expressed in slow potentials and as measured from frontal and parietal electrodes. This study shows how the causal effects of brain states on neural processes can be studied without the confounding influence of experimental task and stimuli.

International Journal of Psychophysiology, 2010

Transcranial magnetic stimulation (TMS) can be used for studying causal effects on visual phenome... more Transcranial magnetic stimulation (TMS) can be used for studying causal effects on visual phenomenology. Occipitally delivered TMS pulses when applied after a brief spatially extended visual reference stimulus induce a localized degrading effect on the visual quality of the reference, a subjective darkening called scotoma. The stability of the subjective characteristics of artificial scotomas has not been studied with advanced neuronavigation of TMS. In 3 experiments we studied the size and relative contrast of TMSinduced scotomas and looked for possible adaptation effects to TMS delivered to the same cortical location for many successive trials. MRI-based neuro-navigated biphasic single-pulse stimulation was used to show that (i) ISI values leading to scotomas in all individual subjects extend over a wide range of time intervals from 35 ms to 199 ms, (ii) the size of and relative decrease of contrast of scotoma area remained stable over multiple stimulations, and (iii) TMS effect on scotomas was location-specific so that carry-over effects from temporarily changed TMS location to another hemisphere were absentreturning back with stimulation to the original site from a temporarily changed site led to the previous value of scotoma expression.