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Submitted manuscript version. Published version available in Tracking changes in spatial frequency sensitivity during natural image processing in school-age: an event-related potential study (2018) 166, s. 664-678. Several studies have shown that behavioral and electrophysiological correlates of processing visual images containing low or high spatial frequency (LSF or HSF) information undergo development after early childhood. However, the maturation of spatial frequency sensitivity in school-age has been investigated using abstract stimuli only. The aim of the current study was to assess how LSF and HSF features affect the processing of everyday photographs at the behavioral and electrophysiological levels in children aged 7-15 years and adults. We presented grayscale images containing either animals or vehicles and their luminance-matched modified versions filtered at low or high spatial frequencies. Modulations of classification accuracy, reaction time and visual event-related potentials (posterior P1 and N1 components) were compared across five developmental groups and three image types. We found disproportionately worse response accuracies for LSF stimuli relative to HSF images in children aged 7-8 years, an effect that was accompanied by smaller LSF-evoked P1 amplitudes in this age period. At 7-8 years of age, P1 and N1 amplitudes were modulated by HSF and LSF stimuli (P1: HSF>LSF; N1: LSF>HSF), with a gradual shift towards the opposite pattern (P1: LSF>HSF; N1: HSF>LSF) with increasing age. Our results indicate that early cortical processing of both spatial frequency ranges undergo substantial development in school-age, with a relative delay of LSF analysis, and underline the utility of our paradigm in tracking the maturation of LSF vs. HSF sensitivity in this age group.

In healthy humans, passage reading depends upon a critical organizing role played by the magnocellular/dorsal visual pathway. In a recent study, we found a significant correlation between orthographic reading deficits in schizophrenia and deficits in contrast sensitivity to low spatial frequency stimuli, suggesting an underlying magnocellular processing abnormality. The interrelationship between magnocellular dysfunction and passage reading impairments in schizophrenia was investigated in 21 patients with schizophrenia and 17 healthy control volunteers using behavioral and functional MRI (fMRI) based measures. fMRI activation patterns during passage- and single-word reading were evaluated in relation to cortical areas with differential sensitivity to low versus high spatial frequency cortical regions indentified using a phase-encoded fMRI paradigm.On average, patients with schizophrenia read at the 6th grade level, despite completion of more than 12years of education and estimated normal pre-morbid IQ. Schizophrenia patients also showed significantly impaired contrast sensitivity to low spatial frequencies and abnormal neural activity in response to stimulation with low spatial frequencies, consistent with dysfunction of magnocellular processing. Further, these magnocellular deficits were predictive of poor performance on a standardized psychoeducational test of passage reading. These findings suggest that reading is an important index of cognitive dysfunction in schizophrenia and highlight the contribution of magnocellular dysfunction to overall cognitive impairments in schizophrenia.

The pulsed-pedestal paradigm consists of the simultaneous brief presentation of a test stimulus and luminance pedestals. Processing with this paradigm is thought to be mediated by the parvocellular pathway. The steady-pedestal paradigm consists of the brief presentation of a test stimulus against a continuously presented luminance pedestals. Processing with this paradigm is thought to be mediated by the magnocellular pathway. To test the prediction that transient attention should have a differential effect on performance with these two paradigms, we added to their typical procedures peripheral precues that trigger transient attention. As expected, we have found that the attraction of transient attention to the target location improved performance with the pulsed-pedestal paradigm, but had no reliable effect on performance with the steady-pedestal paradigm. These findings support the hypothesis that transient attention favors parvocellular over magnocellular processing.

To evaluate whether luminance contrast discrimination losses in amblyopia on putative magnocellular (MC) and parvocellular (PC) pathway tasks reflect deficits at retinogeniculate or cortical sites. Fifteen amblyopes including six anisometropes, seven strabismics, two mixed and 12 age-matched controls were investigated. Contrast discrimination was measured using established psychophysical procedures that differentiate MC and PC processing. Data were described with a model of the contrast response of primate retinal ganglion cells. All amblyopes and controls displayed the same contrast signatures on the MC and PC tasks, with three strabismics having reduced sensitivity. Amblyopic PC contrast gain was similar to electrophysiological estimates from visually normal, non-human primates. Sensitivity losses evident in a subset of the amblyopes reflect cortical summation deficits, with no change in retinogeniculate contrast responses. The data do not support the proposal that amblyopic contrast sensitivity losses on MC and PC tasks reflect retinogeniculate deficits, but rather are due to anomalous post-retinogeniculate cortical processing of retinal signals.

Visual processing deficits in dyslexic readers are argued to evolve as a consequence of reading failure. This study examines dorsal stream functioning of children before they commence formal reading instruction to determine whether visual deficits precede reading difficulties. Coherent motion and visual frequency doubling detection were measured in children at familial risk for dyslexia and in children unselected for family reading history. Here we show that children who are at family risk for dyslexia demonstrate dorsal stream deficits before they learn to read, whilst demonstrating no corresponding deficits in coherent form and static grating control tasks. Results indicate that the dorsal visual deficits observed in dyslexic readers are unlikely to be the result of reading failure.

Purpose: Contrast gain signatures of inferred magnocellular and parvocellular postreceptoral pathways were assessed for patients with glaucoma using a contrast discrimination paradigm developed by Pokomy and Smith. The potential causes for changes in contrast gain signature were investigated using model simulations of ganglion cell contrast responses. Methods: Foveal contrast discrimination thresholds were measured with a pedestal-A-pedestal paradigm developed by Pokorny and Smith [Pokorny, J., & Smith, V. C. (1997). Psychophysical signatures associated with magnocellular and parvocellular pathway contrast gain. Journal of the Optical Society of America A, 14(9), 2477-2486]. Stimuli were 27 ms luminance increments superimposed on 227 ms pulsed A-pedestals. Contrast thresholds and contrast gain signatures mediated by the inferred magnocellular (MC) and parvocellular (PC) pathways were assessed using linear fits to contrast discrimination thresholds at either lower or higher A-pedestal contrasts, respectively. Twenty-seven patients with glaucoma were tested, as well as 16 age-similar control subjects free of eye disease. Results: Contrast sensitivity and contrast gain signature mediated by the inferred MC pathway were lower for the glaucoma group, and reduced contrast gain signature was correlated with reduced contrast sensitivity (r 2 =45%, p

Much work in the cognitive neuroscience of schizophrenia has focused on attention, memory, and executive functioning. To date, less work has focused on perceptual processing. However, perceptual functions are frequently disrupted in schizophrenia, and thus this domain has been included in the CNTRICS (Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia) project. In this article, we describe the basic science presentation and the breakout group discussion on the topic of perception from the first CNTRICS meeting, held in Bethesda, Maryland on February 26 and 27, 2007. The importance of perceptual dysfunction in schizophrenia, the nature of perceptual abnormalities in this disorder, and the critical need to develop perceptual tests appropriate for future clinical trials were discussed. Although deficits are also seen in auditory, olfactory, and somatosensory processing in schizophrenia, the first CNTRICS meeting focused on visual processing deficits. Key concepts of gain control and integration in visual perception were introduced. Definitions and examples of these concepts are provided in this article. Use of visual gain control and integration fit a number of the criteria suggested by the CNTRICS committee, provide fundamental constructs for understanding the visual system in schizophrenia, and are inclusive of both lower-level and higher-level perceptual deficits.

It is well established that sensitivity is not necessarily equivalent at isoeccentric locations across the visual field. The focus of this study was a psychophysical examination of the spatial sensitivity differences between the upper and lower visual hemifields under conditions biased toward the presumed magnocellular or parvocellular visual pathway. Experiment 1 showed higher contrast sensitivity in the lower visual field when visual sensitivity was biased toward the parvocellular pathway; no visual field anisotropy was found when sensitivity was biased toward the magnocellular pathway. Experiment 2 showed that the magnitude of the contrast sensitivity anisotropy within the presumed parvocellular pathway increased when test targets of higher spatial frequency were used. The results of this study have relevance for the design both of psychophysical paradigms and clinical training programs for patients with heterogeneous visual field loss.

This study examined the extent to which letter optotypes and grating stimuli provide equivalent measures of contrast sensitivity under conditions designed to favor the magnocellular (MC) and parvocellular (PC) pathways. The contrast sensitivity functions (CSFs) of three visually normal observers were measured for Sloan letters and Gabor patches, using steady- and pulsed-pedestal paradigms to bias processing toward MC and PC pathways, respectively. CSFs for Gabor patches were low-pass for the steady-pedestal paradigm and band-pass for the pulsed-pedestal paradigm, in agreement with previous reports. However, CSFs for letters were low-pass for both testing paradigms. CSFs for letters restricted in frequency content by spatial filtering were equivalent to those for Gabor patches for both testing paradigms. Results indicate that conventional letter optotypes can provide a misleading measure of contrast sensitivity, especially under conditions emphasizing the PC pathway. The use of spatially band-pass filtered letters can provide a more appropriate evaluation of spatial contrast sensitivity while maintaining some of the potential advantages of letters.

We measured contrast thresholds for perception of the Hermann grid illusion, using different contrast polarities and mean luminances, in dyslexics and non-dyslexics. Both groups of subjects gave significantly lower thresholds with grids having dark squares and light paths, but there was no significant threshold difference between groups. Perceived strength of illusion was also measured in grids at suprathreshold contrast levels. Dyslexics perceived the illusion to be significantly stronger than non-dyslexics when the grid had light paths and low luminance.

The effects of transient spatial attention on temporal resolution were recently studied and compared with attentional effects on spatial resolution. It was found that in contrast to the attentional enhancement of spatial resolution, transient attention impairs temporal resolution. To account for these findings a novel attentional mechanism was suggested. This attentional mechanism facilitates parvocellular neurons at the attended location, which in turn inhibit the activity of magnocellular neurons at the same location [Yeshurun & Levy, Psychol. Sci. 14 (3) (2003a) 225]. The goal of the present study was to replicate the attentional decrement in temporal resolution (Experiment 1), and perform direct tests of this `parvo facilitation––magno inhibition' hypothesis. The employment of isoluminant stimuli (Experiments 2a and 2b) or a red background (Experiment 3) ensured that the parvo system was the main system mediating performance. Consequently, any parvo–magno inhibitory processes elicited by the attentional mechanism should only have a minor effect on performance. As predicted, these manipulations either significantly attenuated or completely eliminated the attentional decrement in temporal resolution. These findings provide direct support to the hypothesis that attention favors parvocellular over magnocellular neurons.

The goal of this study was to establish the spatial summation properties associated with inferred PC- and MC-pathway mediated psychophysical contrast discrimination. Previous work has established two paradigms that reveal characteristic signatures of these pathways. In the pulse paradigm, a four-square array was pulsed briefly, on a constant background. In the steady-pedestal paradigm, the stimulus array was presented continuously as a steady-pedestal within a constant surround. In both paradigms, one square differed from the others, giving the observer a forced choice spatial discrimination task. Area summation functions derived for the pulse paradigm decreased with area, with a slope of −0.25 on a log–log axis. Area summation functions derived for the steady-pedestal paradigm decreased as a power function of area, approaching an asymptote above one square degree. The latter are consistent with the classical data of threshold spatial summation.

Displacement thresholds with incremental chromatic and luminance edges were measured on different backgrounds. Above 3% luminance contrast, thresholds were always similar. At luminance contrasts below 3%, luminance edges could not be detected, but chromatic edges were still visible. At these low contrasts displacement thresholds for chromatic edges increased to a high level. We interpret these data in terms of multiple mechanisms; above 3% contrast a luminance mechanism determines thresholds, but when, at lower contrasts, chromatic mechanisms support detection, they also support the spatial task. Physiological data were consistent with the different mechanisms originating at the retinal ganglion cell level.

The topographic electroretinogram evoked by multi-focal exchange of black and white or red and green stimuli was analysed into linear and non-linear Wiener kernels. The first-order (temporally linear) response showed a biphasic waveform which inverted as the luminance ratio of the exchanged colours passed through unity (established both psychophysically and photometrically). A short latency non-linearity which was dependant on luminance contrast was observed in both chromatic and achromatic ERG. However, in the chromatic second-order response, a long-latency non-linearity, foveally prominent, with a distinct skew in power towards the nasal retina, appeared around the isoluminant point, between the points of silent substitution for the L and M-cone types. Modelling of the second-order responses showed that over a wide range of luminance ratios, the chromatic ERG is well described by a linear combination of the achromatic (contrast-dependent) component and the response at isoluminance. The difference in second-order response between coloured and black and white stimulation, at the same luminance contrast, showed that the long-latency non-linearity is recorded when the red and green cone types are operating out of phase and peaks in amplitude at a green/red luminance ratio of 0.8. This interpretation was confirmed by the lack of the long-latency non-linearity in colour-anomalous subjects (whether deficient in the L or the M-cone type). A marked similarity exists between the properties of the long-latency non-linearity and the frequency-doubled response generated in the ganglion cells of the magnocellular pathway.

The strength of rod inputs to ganglion cells was assessed in the macaque retina at retinal positions within 3–15 deg eccentricity. The experimental paradigm used temporally modulated heterochromatic lights whose relative phase was varied. This paradigm provided a sensitive test to detect rod input. In parvocellular (PC) pathway cells, the gain of the cone-driven signal decreased with decrease in luminance. At 2 td a weak rod response, of a few impulses per second for 100% rod modulation, was revealed in about 60% of cells. For blue-on cells, the cone-driven response also decreased with retinal illuminance, but no rod response could be found. In magnocellular (MC) pathway cells, rod input was much more apparent. Responses became rod dominated at and below 20 td; we cannot exclude rod intrusion at higher retinal illuminances. Responsivity was maintained even at low retinal illuminances. Temporal-frequency dependent rod-cone interactions were observed in MC-pathway cells. Rod responses were of longer latency than cone responses, but there was no evidence of any difference in rod latency between parvocellular and magnocellular pathways.

Foveal pathway visual function was assessed in 11 patients having tumours extending into the suprasellar region but without evidence of visual impairment as assessed by visual acuity and Bjerrum screen campimetry. Psychophysical and routine visual evoked potential (VEP) measurements were obtained from the eye ipsilateral to the maximal suprasellar extension. The sensitivity of luminance and chromatic pathways was assessed psychophysically by measuring increment thresholds for white and red flashes of light presented on a white adapting field. Temporal sensitivity was assessed psychophysically by measuring threshold modulation sensitivity for sinusoidally modulating stimuli (de Lange attenuation characteristic). The patient group showed approximately equal significant psychophysical losses in chromatic, luminance and temporal sensitivities relative to normal controls. Midline VEP P100 latencies of the patient group did not significantly differ from those of the normal control group. It is concluded that tumours extending into the suprasellar region can cause foveal pathway dysfunction affecting both magno- and parvo-cellular pathways, even in the presence of normal visual acuity and fields suggesting a more widespread and insidious abnormality of the visual pathways in this condition than previously thought.

Previous studies have identified a magnocellular pathway defect in approximately 75 % of dyslexics. Since these experiments have not classified dyslexia into subtypes, the purpose of this experiment was to determine if adult dyseidetic dyslexics or dysphoneidetic dyslexics suffer from a defect in the magnocellular pathway. Nine dyseidetic dyslexics, eight dysphoneidetic dyslexics, and nine normal readers participated in the experiment. Contrast sensitivity functions (CSF) were determined with vertically oriented sine wave gratings (0.5, 1.0, 2.0, 4.0, 8.0, 12.0 c/deg drifting at 1 and 10 Hz) by employing a two-alternative, forced-choice technique. The results of the experiment indicated that dysphoneidetic dyslexics had reduced sensitivity to low spatial frequencies at 10 Hz, whereas dyseidetic dyslexics did not have reduced sensitivity at either 1 or 10 Hz. These results suggest that the type of dyslexia influences whether losses in perception are found which are consistent with a magnocellular deficit.

Developmental dyslexics perform differently from controls on a number of low level visual tasks. We carried out three experiments to explore some of these differences. Dyslexics have been found to have reduced luminance contrast sensitivity at mesopic luminance levels. We failed to replicate this finding at photopic luminance levels. We also compared the (photopic) coherent motion detection thresholds of groups of child and adult dyslexics with those of age matched controls. Dyslexics were significantly less sensitive to motion. The results are discussed in relation to a recent suggestion that developmental dyslexia may be associated with a magnocellular visual deficit.

This study deals with the effect of stimulus contrast, between 1.3% and 96%, on the visual evoked potentials (VEPs) for onset of motion and for pattern reversal of checkerboard stimuli. The VEPs for pattern reversal and for the onset of motion both contain an initial positive peak (P1; peak latency about 120 msec) followed by a later negative peak (N2; peak latency 160–200 msec). However the P1 peak dominates the pattern-reversal VEP when recorded from the midline occipital lead, where it is maximal, while the N2 peak is larger in the motion-onset VEP, especially when recorded from unipolar lateral occipital leads. Whereas the amplitude of the P1 peak in both the pattern-reversal VEP and the motion-onset VEP decreases with decreasing contrast (becoming undetectable at a contrast of about 2% for the motion-onset VEP), the amplitude of the N2 peak in both types of VEP does not vary significantly with contrast, above a contrast of 1.3%. The increase in peak latency with decreasing contrast is also more pronounced for the positive than the negative peaks of both types of VEP. Taking into account the high contrast sensitivity of the magnocellular system (thought to be involved in the processing of motion) compared with the parvocellular system (probably more concerned with the processing of form), our findings suggest that for both motion-onset and pattern-reversal VEPs the negative peak is attributable to the motion-processing magnocellular pathway and the positive peak to the form-processing parvocellular system.