Perceptual phenomenology

I am looking at an apple. The apple has a lot of properties and some, but not all, of these are part of my phenomenology at this moment: I am aware of these properties. And some, but not all, of these properties that I am aware of are part of my perceptual (or sensory) phenomenology. If I am attending to the apple’s color, this property will be part of my perceptual phenomenology. The property of being a granny smith apple from Chile is unlikely to be part of my perceptual phenomenology. Here are two problems for anyone who is interested in conscious experience in general, and perceptual experience in particular: (a) How can we tell which properties are part of our phenomenology and which ones are not? (b) How can we tell which properties are part of our perceptual phenomenology and which ones are part of our non-perceptual phenomenology? I will focus on (b) in this paper. My aim is twofold: I propose a methodology for answering the question of which properties are part of our perceptual phenomenology and I provide an example for how this methodology could be applied

Too little, too late: reduced visual span and speed characterize pure alexia

Whether normal word reading includes a stage of visual processing selectively dedicated to word or letter recognition is highly debated. Characterizing pure alexia, a seemingly selective disorder of reading, has been central to this debate. Two main theories claim either that 1) Pure alexia is caused by damage to a reading specific brain region in the left fusiform gyrus or 2) Pure alexia results from a general visual impairment that may particularly affect simultaneous processing of multiple items. We tested these competing theories in 4 patients with pure alexia using sensitive psychophysical measures and mathematical modeling. Recognition of single letters and digits in the central visual field was impaired in all patients. Visual apprehension span was also reduced for both letters and digits in all patients. The only cortical region lesioned across all 4 patients was the left fusiform gyrus, indicating that this region subserves a function broader than letter or word identification. We suggest that a seemingly pure disorder of reading can arise due to a general reduction of visual speed and span, and explain why this has a disproportionate impact on word reading while recognition of other visual stimuli are less obviously affected

Pupil dilation reveals top–down attentional load during spatial monitoring

It has long been known that the diameter of human pupil enlarges with increasing effort during the execution of a task. This has been observed not only for purely mechanical effort but also for mental effort, as for example the computation of arithmetic problems with different levels of difficulty. Here we show that pupil dilation reflects changes in visuospatial awareness induced by attentional load during multi-tasking. In the single-task condition, participants had to report the position of lateralized, briefly presented, masked visual targets ("right", "left", or "both" sides). In the multitasking conditions, participants also performed additional tasks, either visual or auditory, to increase the attentional load. Sensory stimulation was kept constant across all conditions to rule out the influence of low-level factors. Results show that event-related pupil dilation strikingly increased with task demands, mirroring a concurrent decrease in visuospatial awareness. Importantly, pupil dilation significantly differed between two dual-task conditions that required to process the same number of stimuli but yielded differed levels of accuracy (difficulty). In contrast, pupil dilation did not differ between two conditions which were equally challenging but differed both in the modality of the dual task (auditory vs. visual) and in the number of stimuli to be attended. We conclude that pupil dilation genuinely reflects the top-down allocation of supramodal attentional resources

Different effects of dual task demands on the speech of young and older adults

This is an electronic version of an article published in Kemper, S., Herman, R. E., Nartowicz, J.(2005). Different effects of dual task demands on the speech of young and older adults. Aging, Neuropsychology, and Cognition, 12, 340-358. PM#1410812. Aging, Neuropsychology, and Cognition is available online at www.taylorandfrancis.comYoung and older adults provided language samples in response to elicitation questions while concurrently performing 3 different tasks. The language samples were scored on three dimensions: fluency, grammatical complexity, and content. Previous research has shown that older adults use a restricted speech register that is grammatically less complex than young adults’ and has suggested that this restricted speech register is buffered from the costs of dual task demands. This hypothesis was tested by comparing language samples collected during a baseline condition with those produced while the participants were performing the concurrent tasks. The results indicate that young and older adults adopt different strategies when confronted with dual task demands. Young adults shift to a restricted speech register when confronted with dual task demands. Older adults, who were already using a restricted speech register, became less fluent although the grammatical complexity and informational content of their speech was preserved. Hence, some but not all aspects of older adults’ speech are buffered from dual task demands

Bisecting the mental number line in near and far space

Much evidence suggests that common posterior parietal mechanisms underlie the orientation of attention in physical space and along the mental number line. For example, the small leftward bias (pseudoneglect) found in paper-and-pencil line bisection is also found when participants "bisect" number pairs, estimating (without calculating) the number midway between two others. For bisection of physical lines, pseudoneglect has been found to shift rightward as lines are moved from near space (immediately surrounding the body) to far space. We investigated whether the presentation of stimuli in near or far space also modulated spatial attention for the mental number line. Participants bisected physical lines or number pairs presented at four distances (60, 120, 180, 240 cm). Clear rightward shifts in bias were observed for both tasks. Furthermore, the rate at which this shift occurred in the two tasks, as measured by least squares regression slopes, was significantly correlated across participants, suggesting that the transition from near to far distances induced a common modulation of lateral attention in physical and numerical space. These results demonstrate a tight coupling between number and physical space, and show that even such prototypically abstract concepts as number are modulated by our on-line interactions with the world

Effects of Age of Onset of Tonic-Clonic Seizures on Neuropsychological Performance in Children

Forty-eight children (aged 9 to 15 years) with tonic-clonic seizures were administered a neuropsychological test battery. The children with seizures of early onset (before age 5) were significantly impaired relative to the children with later onset on 8 of the 14 measures in the battery. The deficits were seen on tasks whose requirements included the repetition of a simple motor act, attention and concentration, memory, and complex problem solving. These findings emphasize the need for further research to determine the causal factors of the greater dysfunction seen in the early onset group. RÉSUMÉ Quarante huit enfants ÁgÉs de 9 À 15 ans souffrant de crises Épileptiques tonico-cloniques ont ÉtÉÉtudiÉs avec une batterie de tests neuropsychologiques. Pour huit des quatorze mesures de cette batterie de tests les enfants dont les cirses avaient dÉbutÉ prÉcocÉment (avant cinq ans) se sont avÉrÉs Étre signiflcativement dÉtÉriorÉs par rapport À ceux dont les crises avaient dÉbutÉ plus tardivement. Les dÉficits se sont manifestÉs pour des tÁches nÉcessitant la rÉpÉtition d'un acte moteur simple, attention et concentration, mÉmoire et capacitÉÀ rÉsoudre des problÈmes complexes. Ces rÉsultats mettent l'accent sur la nÉcessitÉ de poursuivre les recherches afin de dÉterminer les facteurs responsables de la plus grande dysfonction observÉe chez les enfants dont l'Épilepsie a dÉbutÉ tÔt dans la vie. RESUMEN Se ha aplicado una bateria de tests neuro-psicolÓgicos a 48 niÑos de 9 a 15 aÑos de edad que padecÍan ataques tonico-clÓnicos. Los niÑos con ataques de comienzo precoz (antes de los 5 aÑos) mostraron incapacidades significativas compareÁndolos con niÑos con comienzos mÁs tardios en 8 de los 14 tests de la bateria. Los defectos fueron detectados en las pruebas cuyos requisitos incluÍan la repeticiÓn de un acto motor simple, atenciÓn y concentraciÓn, memoria y resoluciÓn de problemas complejos. Estos hallazgos indican la necesidad de continuar la inves-tigaciÓn para determinar los factores causales de la mayor disfunciÓn observada en el grupo de comienzo precoz. ZUSAMMENFASSUNG 48 Kinder (9 bis 15 Jahre alt) mit tonisch-klonischen KrÄmpfen wurden mit einer neuropsychologischen Testbatterie untersucht. Die Kinder mit einem FrÜhbeginn der AnfÄlle (vor dem Alter von 5 Jahren) zeigten sich bei 8 von 14 Tests der Serie deutlich beeintrÄchtigt im VerhÄltnis zu Kindern mit spÄterem Anfallsbeginn. Die Defekte traten bei Aufgaben auf, die folgende AnsprÜche stellten: Wiederholung einer einfachen motorischen Handlung, Aufmerksamkeit und Konzentration, GedÄchtnis und komplexes ProblemlÖsen. Diese Befunde deuten auf die Notwendigkeit weiterer Untersuchungen, um die ursÄchlichen Faktoren der grÖßeren Funktionseinbuße zu bestimmen, die bei Patienten mit frÜhem Anfallsbeginn beobachtet wird.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65238/1/j.1528-1157.1981.tb04102.x.pd

Functional imaging reveals rapid reorganization of cortical activity after parietal inactivation in monkeys

Impairments of spatial awareness and decision making occur frequently as a consequence of parietal lesions. Here we used event-related functional MRI (fMRI) in monkeys to investigate rapid reorganization of spatial networks during reversible pharmacological inactivation of the lateral intraparietal area (LIP), which plays a role in the selection of eye movement targets. We measured fMRI activity in control and inactivation sessions while monkeys performed memory saccades to either instructed or autonomously chosen spatial locations. Inactivation caused a reduction of contralesional choices. Inactivation effects on fMRI activity were anatomically and functionally specific and mainly consisted of: (i) activity reduction in the upper bank of the superior temporal sulcus (temporal parietal occipital area) for single contralesional targets, especially in the inactivated hemisphere; and (ii) activity increase accompanying contralesional choices between bilateral targets in several frontal and parieto-temporal areas in both hemispheres. There was no overactivation for ipsilesional targets or choices in the intact hemisphere. Task-specific effects of LIP inactivation on blood oxygen level-dependent activity in the temporal parietal occipital area underline the importance of the superior temporal sulcus for spatial processing. Furthermore, our results agree only partially with the influential interhemispheric competition model of spatial neglect and suggest an additional component of interhemispheric cooperation in the compensation of neglect deficits

Spatial attention: differential shifts in pseudoneglect direction with time-on-task and initial bias support the idea of observer subtypes

<p>Asymmetry in human spatial attention has long been documented. In the general population the majority of individuals tend to misbisect horizontal lines to the left of veridical centre. Nonetheless in virtually all previously reported studies on healthy participants, there have been subsets of people displaying rightward biases.</p> <p>In this study, we report differential time-on task effects depending on participants' initial pseudoneglect bias: participants with an initial left bias in a landmark task (in which they had to judge whether a transection mark appeared closer to the right or left end of a line) showed a significant rightward shift over the course of the experimental session, whereas participants with an initial right bias shifted leftwards.</p> <p>We argue that these differences in initial biases as well as the differential shifts with time-on task reflect genuine observer subtypes displaying diverging behavioural patterns. These observer subtypes could be driven by differences in brain organisation and/or lateralisation such as varying anatomical pathway asymmetries. </p&gt

Microstructural damage of the posterior corpus callosum contributes to the clinical severity of neglect

One theory to account for neglect symptoms in patients with right focal damage invokes a release of inhibition of the right parietal cortex over the left parieto-frontal circuits, by disconnection mechanism. This theory is supported by transcranial magnetic stimulation studies showing the existence of asymmetric inhibitory interactions between the left and right posterior parietal cortex, with a right hemispheric advantage. These inhibitory mechanisms are mediated by direct transcallosal projections located in the posterior portions of the corpus callosum. The current study, using diffusion imaging and tract-based spatial statistics (TBSS), aims at assessing, in a data-driven fashion, the contribution of structural disconnection between hemispheres in determining the presence and severity of neglect. Eleven patients with right acute stroke and 11 healthy matched controls underwent MRI at 3T, including diffusion imaging, and T1-weighted volumes. TBSS was modified to account for the presence of the lesion and used to assess the presence and extension of changes in diffusion indices of microscopic white matter integrity in the left hemisphere of patients compared to controls, and to investigate, by correlation analysis, whether this damage might account for the presence and severity of patients' neglect, as assessed by the Behavioural Inattention Test (BIT). None of the patients had any macroscopic abnormality in the left hemisphere; however, 3 cases were discarded due to image artefacts in the MRI data. Conversely, TBSS analysis revealed widespread changes in diffusion indices in most of their left hemisphere tracts, with a predominant involvement of the corpus callosum and its projections on the parietal white matter. A region of association between patients' scores at BIT and brain FA values was found in the posterior part of the corpus callosum. This study strongly supports the hypothesis of a major role of structural disconnection between the right and left parietal cortex in determining 'neglect'

Crossmodal visual-tactile extinction: Modulation by posture implicates biased competition in proprioceptively reconstructed space

Extinction is a common consequence of unilateral brain injury: contralesional events can be perceived in isolation, yet are missed when presented concurrently with competing events on the ipsilesional side. This can arise crossmodally, where a contralateral touch is extinguished by an ipsilateral visual event. Recent studies showed that repositioning the hands in visible space, or making visual events more distant, can modulate such crossmodal extinction. Here, in a detailed single-case study, we implemented a novel spatial manipulation when assessing crossmodal extinction. This was designed not only to hold somatosensory inputs and hand/arm-posture constant, but also to hold (retinotopic) visual inputs constant, yet while still changing the spatial relationship of tactile and visual events in the external world. Our right hemisphere patient extinguished left-hand touches due to visual stimulation of the right visual field (RVF) when tested in the usual default posture with eyes/head directed straight ahead. But when her eyes/head were turned to the far left (and any visual events shifted along with this), such that the identical RVF retinal stimulation now fell at the same external location as the left-hand touch, crossmodal extinction was eliminated. Since only proprioceptive postural cues could signal this changed spatial relationship for the critical condition, our results show for the first time that such postural cues alone are sufficient to modulate crossmodal extinction. Identical somatosensory and retinal inputs can lead to severe crossmodal extinction, or none, depending on current posture