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PubMed2000

Exercise alters fractal dimension and spatial correlation of pulmonary blood flow in the horse.

We determined the changes in fractal dimensions and spatial correlations of regional pulmonary blood flow with increasing exercise in race horses (n = 4) by using 15-microm fluorescent microspheres. Fluorescence was measured to quantitate regional blood to 1.3-cm(3) samples (n = 1,621-2,503). Perfusion distributions were characterized with fractal dimensions (a measure of spatial variability) and spatial correlations. On average, the fractal dimension decreased with exercise (trot 1.216 to gallop 1.173; P < 0. 05) despite a variable fractal dimension at rest. Spatial correlation of flow to neighboring pieces increased with exercise (trot 0.57 +/- 0.074 to gallop 0.73 +/- 0.051) and was inversely correlated with fractal dimension, indicating better spatial correlation as blood flow distribution becomes more uniform. This is the first study to document a change in fractal dimension as a result of increasing pulmonary blood flow. Spatial differences in response to vasoregulatory mediators may play a role in this phenomenon.

Algorithms↗
PubMed2004

Visual cortex neurons of monkeys and cats: temporal dynamics of the spatial frequency response function.

We measured the responses of striate cortex neurons as a function of spatial frequency on a fine time scale, over the course of an interval that is comparable to the duration of a single fixation (200 ms). Stationary gratings were flashed on for 200 ms and then off for 300 ms; the responses were analyzed at sequential 1-ms intervals. We found that 1) the preferred spatial frequency shifts through time from low frequencies to high frequencies, 2) the latency of the response increases as a function of spatial frequency, and 3) the poststimulus time histograms (PSTHs) are relatively shape-invariant across spatial frequency. The dynamic shifts in preferred spatial frequency appear to be a simple consequence of the latency shifts and the transient nature of the PSTH. The effects of these dynamic shifts on the coding of spatial frequency information are examined within the context of several different temporal integration strategies, and pattern-detection performance is determined as a function of the interval of integration, following response onset. The findings are considered within the context of related investigations as well as a number of functional issues: motion selectivity in depth, "coarse-to-fine" processing, direction selectivity, latency as a code for stimulus attributes, and behavioral response latency. Finally, we demonstrate that the results are qualitatively consistent with a simple feedforward model, similar to the one originally proposed in 1962 by Hubel and Wiesel, that incorporates measured differences in the response latencies and the receptive field sizes of different lateral geniculate nucleus inputs.

Action Potentials↗
PubMed2004

A neuronal correlate of the precedence effect is associated with spatial selectivity in the barn owl's auditory midbrain.

Sound localization in echoic conditions depends on a precedence effect (PE), in which the first arriving sound dominates the perceived location of later reflections. Previous studies have demonstrated neurophysiological correlates of the PE in several species, but the underlying mechanisms remain unknown. The present study documents responses of space-specific neurons in the barn owl's inferior colliculus (IC) to stimuli simulating direct sounds and reflections that overlap in time at the listener's ears. Responses to 100-ms noises with lead-lag delays from 1 to 100 ms were recorded from neurons in the space-mapped subdivisions of IC in anesthetized owls (N2O/isofluorane). Responses to a target located at a unit's best location were usually suppressed by a masker located outside the excitatory portion of the spatial receptive field. The least spatially selective units exhibited temporally symmetric effects, in that the amount of suppression was the same whether the masker led or lagged. Such effects mirror the alteration of localization cues caused by acoustic superposition of leading and lagging sounds. In more spatially selective units, the suppression was often temporally asymmetric, being more pronounced when the masker led. The masker often evoked small changes in spatial tuning that were not related to the magnitude of suppressive effects. The association of temporally asymmetric suppression with spatial selectivity suggests that this property emerges within IC, and not at earlier stages of auditory processing. Asymmetric suppression reduces the ability of highly spatially selective neurons to encode the location of lagging sounds, providing a possible basis for the PE.

Acoustic Stimulation↗
PubMed1988

Spatial and temporal determinants of directionally selective velocity preference in cat striate cortex neurons.

1. Direction-selective properties of neurons in cat striate cortex (area 17) were studied with flashed and continuously moving bar stimuli. Receptive fields were characterized by measurement of static and dynamic parameters, which were correlated with the velocity preference exhibited by the same cells. 2. Each neuron was found to be direction selective to a limited range of velocities. This behavior was characterized by measuring the optimal velocity (Vopt) to elicit responses in the preferred and null directions that were maximally distinct. 3. A bar stimulus flashed sequentially at two nearby locations in the receptive field also produced direction-selective behavior, which was characterized by an optimal displacement (Dopt) to drive maximally distinct responses in the preferred versus null directions. 4. The static spatial receptive field properties were quantified by measurement of the receptive field size (2 sigma) and the spatial subunit wavelength (lambda). The latter quantity was measured as twice the separation between adjacent ON and OFF regions in simple cells and as twice the optimal separation for lateral inhibition between two simultaneously flashed bars in complex cells. 5. Direction-selective velocity preference for continuously moving stimuli, Vopt, was found to be highly correlated with lambda and with the Dopt for 2-flash motion; Vopt was also correlated to a lesser degree with 2 sigma. These results suggest a fundamental linkage between spatial frequency preference, velocity preference, and spatial tuning to 2-flash motion. 6. The range of measured direction-selective velocity preference values (Vopt) spanned about a 100-fold range, whereas the corresponding values of Dopt or lambda spanned substantially smaller ranges. This discrepancy suggested that the dynamic range of velocity preference among cortical neurons might be determined jointly by the measured spatial properties and by a temporal property that covaries with the measured spatial properties. 7. Temporal properties of striate cortical neurons were assessed from responses to flashed stimuli having a prolonged duration ("step responses"). Neurons typically responded in the following manner: after some latency (L), a transient rise in spike frequency occurred, which then adapted to some sustained level. The adaptation dynamics (extent of sustained vs. transient behavior) were quantified by the first-order time constant (AT) of the adaptation decay, and by the ratio of initial transient rise to final sustained level [adaptation ratio (AR)].(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Spatial and temporal response properties of lagged and nonlagged cells in cat lateral geniculate nucleus.

1. It has recently been shown that the X- and Y-cell classes in the A-layers of the cat lateral geniculate nucleus (LGN) are divisible into lagged and nonlagged types. We have characterized the visual response properties of 153 cells in the A-layers to 1) reveal response features that are relevant to the X/Y and lagged/nonlagged classification schemes, and 2) provide a systematic description of the properties of lagged and nonlagged cells as a basis for understanding mechanisms that affect these two groups. Responses to flashing spots and drifting gratings were measured as the contrast and spatial and temporal modulation were varied. 2. X- and Y-cells were readily distinguished by their spatial tuning. Y-cells had much lower preferred spatial frequencies and spatial resolution than X-cells. Within each functional class (X or Y), however, lagged and nonlagged cells were similar in their spatial response properties. Thus the lagged/nonlagged distinction is not one related to the spatial domain. 3. In the temporal domain X- and Y-cells showed little difference in temporal tuning, whereas lagged and nonlagged cells showed distinctive response properties. The temporal tuning functions of lagged cells were slightly shifted toward lower frequencies with optimal temporal frequencies of lagged X-cells averaging an octave lower than those of nonlagged X-cells. Temporal resolution was much lower in lagged X- and Y-cells than in their nonlagged counterparts. 4. The most dramatic differences between lagged and nonlagged cells appeared in the timing of their responses, as measured by the phase of the response relative to the sinusoidal luminance modulation of a spot centered in the receptive field. Response phase varied approximately linearly with temporal frequency. The slope of the phase versus frequency line is a measure of total integration time, which we refer to as visual latency. Lagged cells has much longer latencies than nonlagged cells. 5. The intercept of the phase versus frequency line is a measure of when in the stimulus cycle the cell responds: we refer to this as the intrinsic or absolute phase of the cell. This measure of response timing not only distinguished lagged and nonlagged cells well but also covaried with the sustained or transient nature of cells' responses to flashed stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1993

Spatiotemporal organization of simple-cell receptive fields in the cat's striate cortex. II. Linearity of temporal and spatial summation.

1. We have tested the hypothesis that simple cells in the cat's visual cortex perform a linear spatiotemporal filtering of the visual image. To conduct this study we note that a visual neuron behaves linearly if the responses to small, brief flashes of light are mathematically related, via the Fourier transform, to the responses elicited by sinusoidal grating stimuli. 2. We have evaluated the linearity of temporal and spatial summation for 118 simple cells recorded from the striate cortex (area 17) of adult cats and kittens at ages 4 and 8 wk postnatal. These neurons represent a subset of the population of cells for which we have described the postnatal development of spatiotemporal receptive-field structure in the preceding paper. Spatiotemporal receptive-field profiles are constructed, with the use of a reverse correlation technique, from the responses to random sequences of small bar stimuli that are brighter or darker than the background. Fourier analysis of spatiotemporal receptive-field profiles yields linear predictions of the cells' spatial and temporal frequency tuning. These predicted responses are compared with spatial and temporal frequency tuning curves measured by the use of drifting, sinusoidal-luminance grating stimuli. 3. For most simple cells, there is good agreement between spatial and temporal frequency tuning curves predicted from the receptive-field profile and those measured by the use of sinusoidal gratings. These results suggest that both spatial and temporal summation within simple cells are approximately linear. There is a tendency for predicted tuning curves to be slightly broader than measured tuning curves, a finding that is consistent with the effects of a threshold nonlinearity at the output of these neurons. In some cases, however, predicted tuning curves deviate from measured responses only at low spatial and temporal frequencies. This cannot be explained by a simple threshold nonlinearity. 4. If linearity is assumed, it should be possible to predict the direction selectivity of simple cells from the structure of their spatiotemporal receptive-field profiles. For virtually all cells, linear predictions correctly determine the preferred direction of motion of a visual stimulus. However, the strength of the directional bias is typically underestimated by a factor of about two on the basis of linear predictions. Consideration of the expansive exponential nonlinearity revealed in the contrast-response function permits a reconciliation of the discrepancy between measured and predicted direction selectivity indexes. 5. Overall, these findings show that spatiotemporal receptive-field profiles obtained with the use of reverse correlation may be used to predict a variety of response properties for simple cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Transfer characteristics of lateral geniculate nucleus X neurons in the cat: effects of spatial frequency and contrast.

1. The dependence of signal transfer in the lateral geniculate nucleus (LGN) on stimulus spatial frequency and contrast was investigated by comparing responses of individual X cells with their direct retinal inputs. 2. We used extracellular single-cell recording methods to isolate action potentials (LGN) and S potentials (SPs) from individual neurons in layers A and A1 of anesthetized and paralyzed cats. The stimuli were drifting sinusoidal gratings that were presented at each neuron's preferred orientation. The effects of stimulus spatial frequency and contrast on retinogeniculate signal transfer were determined by comparing the amplitude of the fundamental Fourier responses measured for a cell's action potentials (LGN) and its retinal input (SP) and calculating the transfer ratio (LGN amplitude/SP amplitude) for each stimulus condition. 3. In all units, the LGN response amplitude was lower than that of its retinal input regardless of stimulus spatial frequency. The mean transfer ratio measured at the peak spatial frequency for individual units was 0.56 +/- 0.03 (SE). For the majority of X LGN neurons, however, the efficiency of signal transfer varied considerably with stimulus spatial frequency. The average transfer ratio increased monotonically from 0.08 cycle/deg to near the high cutoff spatial frequency. 4. The effects of stimulus contrast on geniculate signal transfer were far more complex than previously reported and varied substantially between individual neurons. At low stimulus contrasts (< 10%), where all units exhibited linear response characteristics, only one third of our sample showed a monotonic decrease in transfer ratio with increasing stimulus contrast. The remaining two thirds either exhibited proportionately greater signal transfer for higher stimulus contrasts, or signal transfer remained relatively unchanged with increasing stimulus contrasts. When stimulus contrasts exceeded 10%, where response amplitude began to saturate, the transfer ratio was relatively constant in all units and independent of stimulus contrast. 5. Our results demonstrate that signal transfer from retina to visual cortex is regulated by LGN neurons in a stimulus-dependent manner, which appears to reflect the complex interactions between local membrane mechanisms and extraretinal inputs.

Action Potentials↗
PubMed1998

Temporal and spatial response to second-order stimuli in cat area 18.

Temporal and spatial response to second-order stimuli in cat area 18. J. Neurophysiol. 80: 2811-2823, 1998. Approximately one-half of the neurons in cat area 18 respond to contrast envelope stimuli, consisting of a sinewave carrier whose contrast is modulated by a drifting sinewave envelope of lower spatial frequency. These stimuli should fail to elicit a response from a conventional linear neuron because they are designed to contain no spatial frequency components within the cell's luminance-defined frequency passband. We measured neurons' responses to envelope stimuli by varying both the drift rate and spatial frequency of the contrast modulation. These data were then compared with the same neurons' spatial and temporal properties obtained with luminance-defined sinewave gratings. Most neurons' responses to the envelope stimuli were spatially and temporally bandpass, with bandwidths comparable with those measured with luminance gratings. The temporal responses of these neurons (temporal frequency tuning and latency) were systematically slower when tested with envelope stimuli than with luminance gratings. The simplest kind of model that can accommodate these results is one having separate, parallel streams of bandpass processing for luminance and envelope stimuli.

Algorithms↗
PubMed2001

Modification of response functions of cat visual cortical cells by spatially congruent perturbing stimuli.

Responses of cat striate cortical cells to a drifting sinusoidal grating were modified by the superimposition of a second, perturbing grating (PG) that did not excite the cell when presented alone. One consequence of the presence of a PG was a shift in the tuning curves. The orientation tuning of all 41 cells exposed to a PG and the spatial frequency tuning of 83% of the 23 cells exposed to a PG showed statistically significant dislocations of both the response function peak and center of mass from their single grating values. As found in earlier reports, the presence of PGs suppressed responsiveness. However, reductions measured at the single grating optimum orientation or spatial frequency were on average 1.3 times greater than the suppression found at the peak of the response function modified by the presence of the PG. Much of the loss in response seen at the single grating optimum is thus a result of a shift in the tuning function rather than outright suppression. On average orientation shifts were repulsive and proportional (approximately 0.10 deg/deg) to the angle between the perturbing stimulus and the optimum single grating orientation. Shifts in the spatial frequency response function were both attractive and repulsive, resulting in an overall average of zero. For both simple and complex cells, PGs generally broadened orientation response function bandwidths. Similarly, complex cell spatial frequency response function bandwidths broadened. Simple cell spatial frequency response functions usually did not change, and those that did broadened only 4% on average. These data support the hypothesis that additional sinusoidal components in compound stimuli retune cells' response functions for orientation and spatial frequency.

Algorithms↗
PubMed2000

Auditory and visual spatial localization deficits following bilateral parietal lobe lesions in a patient with Balint's syndrome.

Lesion and electrophysiological studies indicate that the parietal lobes play a role in visual spatial attention and in computing the spatial coordinates of visual input. Fewer studies have investigated the role of the parietal lobe in auditory spatial processing, and an extensive comparison of visual and auditory spatial processing in humans with parietal lobe lesions has yet to be conducted. We have studied such localization abilities in a Balint's syndrome patient (RM) who has bilateral parietal lobe lesions. The results indicated that this patient had a significant deficit in both visual and auditory localization relative to age-matched controls. Unlike the controls, however, RM's auditory localization ability either matched or exceeded his visual localization ability depending on the task. Accordingly, RM exhibited "auditory capture," but not "visual capture" under conditions where control subjects showed the opposite pattern. These results are consistent with hypotheses that the parietal lobes are involved in creating multiple spatial representations and in shifting from one spatial reference point to another, but suggest that these parietal structures are not necessary for the integration of multiple sensory stimuli resulting in capture effects.

Acoustic Stimulation↗
PubMed2000

Activity in human frontal cortex associated with spatial working memory and saccadic behavior.

We examined, with event-related fMRI, two hypotheses about the organization of human working memory function in frontal cortex: (1) that a region immediately anterior to the frontal eye fields (FEF) (superior frontal cortex, SFC) is specialized for spatial working memory (Courtney, et al., 1998); and (2) that dorsolateral prefrontal cortex (PFC) plays a privileged role in the manipulation of spatial stimuli held in working memory (Owen, et al., 1996; Petrides 1994). Our delayed-response task featured 2-D arrays of irregularly arranged squares that were highlighted serially in a random sequence. The Forward Memory condition required maintenance of the spatio-temporal sequence, the Manipulate Memory condition required reordering this sequence into a new spatially defined order, the Guided Saccade condition required saccades to highlighted squares in the array, but no memory, and the Free Saccade condition required self-paced, horizontal saccades. The comparison of fMRI signal intensity associated with 2-D saccade generation (Guided Saccades) versus fMRI signal intensity associated with the delay period of the working memorials condition revealed no evidence for greater working memory-related activity than saccade-related activity in SFC in any individual subject, nor at the level of the group, and greater 2-D saccade than delay-period activity in three of five subjects. These results fail to support the hypothesis that spatial working memory-related activity is represented preferentially in a region of SFC anterior to the FEF (Courtney, et al., 1998). The comparison of maintenance versus manipulation of spatio-temporal information in working memory revealed significantly greater activity associated with the latter in dorsolateral PFC, but not in ventrolateral PFC or in SFC. These results suggest that the delay-related function of SFC is limited to the maintenance of spatial information, and that this region does not support the nonmnemonic executive control functions supported by dorsolateral PFC. These results also indicate that the preferential recruitment of dorsolateral PFC for the manipulation of information held in working memory applies to tasks employing spatial stimuli, as well as to tasks employing verbal stimuli (D'Esposito, et al., 1999); Petrides et al., 1993; Postle et al., 1999).

Acoustic Stimulation↗
PubMed2002

Acoustical vision of neglected stimuli: interaction among spatially converging audiovisual inputs in neglect patients.

Cross-modal spatial integration between auditory and visual stimuli is a common phenomenon in space perception. The principles underlying such integration have been outlined by neurophysiological and behavioral studies in animals (Stein & Meredith, 1993), but little evidence exists proving that similar principles occur also in humans. In the present study, we explored such possibility in patients with visual neglect, namely, patients with visuospatial impairment. To test this hypothesis, neglect patients were required to detect brief flash of light presented in one of six spatial positions, either in a unimodal condition (i.e., only visual stimuli were presented) or in a cross-modal condition (i.e., a sound was presented simultaneously to the visual target, either at the same spatial position or at one of the remaining five possible positions). The results showed an improvement of visual detection when visual and auditory stimuli were originating from the same position in space or at close spatial disparity (16 degrees ). In contrast, no improvement was found when the spatial separation of visual and auditory stimuli was larger than 16 degrees. Moreover, the improvement was larger for visual positions that were more affected by the spatial impairment, i.e., the most peripheral positions in the left visual field (LVF). In conclusion, the results of the present study considerably extend our knowledge about the multisensory integration, by showing in humans the existence of an integrated visuoauditory system with functional properties similar to those found in animals.

Acoustic Stimulation↗
PubMed2004

Involvement of the superior temporal cortex and the occipital cortex in spatial hearing: evidence from repetitive transcranial magnetic stimulation.

The processing of auditory spatial information in cortical areas of the human brain outside of the primary auditory cortex remains poorly understood. Here we investigated the role of the superior temporal gyrus (STG) and the occipital cortex (OC) in spatial hearing using repetitive transcranial magnetic stimulation (rTMS). The right STG is known to be of crucial importance for visual spatial awareness, and has been suggested to be involved in auditory spatial perception. We found that rTMS of the right STG induced a systematic error in the perception of interaural time differences (a primary cue for sound localization in the azimuthal plane). This is in accordance with the recent view, based on both neurophysiological data obtained in monkeys and human neuroimaging studies, that information on sound location is processed within a dorsolateral "where" stream including the caudal STG. A similar, but opposite, auditory shift was obtained after rTMS of secondary visual areas of the right OC. Processing of auditory information in the OC has previously been shown to exist only in blind persons. Thus, the latter finding provides the first evidence of an involvement of the visual cortex in spatial hearing in sighted human subjects, and suggests a close interconnection of the neural representation of auditory and visual space. Because rTMS induced systematic shifts in auditory lateralization, but not a general deterioration, we propose that rTMS of STG or OC specifically affected neuronal circuits transforming auditory spatial coordinates in order to maintain alignment with vision.

Acoustic Stimulation↗
PubMed1999

Categorical and metric spatial processes distinguished by task demands and practice.

In this study we examined Kosslyn's (1987) claim that the right hemisphere exhibits a relative superiority for processing metric spatial relations, whereas the left hemisphere exhibits a relative superiority for processing categorical spatial relations. In particular, we examined whether some failures to observe strong visual field (VF) advantages in previous studies might be due to practice effects that allowed individuals to process tasks in alternative manners (e.g., to process a metric task using a categorical strategy). We used two versions of a task previously employed by Hellige and Michimata (1989)in which individuals judge the metric (distance) or categorical (above/below) spatial relations between a bar and a dot. In one version, the position of the bar was held static. In another, the bar's position varied. This manipulation prevented participants from using the computer screen as a reference frame, forcing them to compute the spatial relationships on the basis of the relevant items only (i.e., the bar and the dot). In the latter, but not the former version of the task we obtained evidence supporting Kosslyn's hypothesis, namely, a significant right visual field (RVF) advantage for categorical spatial processing and a trend toward a left visual field (LVF) advantage for metric spatial processing. Furthermore, the pattern of results for trials on which information was presented centrally (CVF trials) was similar to that observed on RVF trials, whereas the pattern for trials in which identical information was presented in each visual field (BVF trials) was similar to that observed on LVF trials. Such a pattern is consistent with Kosslyn's suggestion that categorical processing is better suited for cells with small receptive fields and metric processing for cells with larger receptive fields.

Adult↗
PubMed1989

The use of fractal image statistics in the estimation of lateral spatial extent.

It has been argued that the characteristics of many commonly occurring surface textures are such that the resulting luminance distributions have the statistical properties of fractals, over a wide range of spatial scales. We show that, when fractal luminance distributions are spatially filtered, the spatial density of zero-crossings obtained is inversely proportional to the scale of filtering, and is not strongly dependent on the fractal dimension of the pattern used. We propose that this predictable property of natural images could provide a basis for the estimation of lateral spatial extent by counting zero-crossings within an interval at a variety of spatial scales, and averaging over spatial scale. We carried out experiments to compare the relative apparent lateral extents of fractal patterns and patterns of equally spaced bars, as a function of the number of bars. The results are in good agreement with theory.

Humans↗
PubMed1994

The effect of similarity and duration on spatial interaction in peripheral vision.

Spatial interactions are extensive in the peripheral visual field, extending up to about half the retinal eccentricity of the target (Toet and Levi, Vision Res. 32, 1349-1357, 1992). In the present study it is shown that the degree and extent of peripheral spatial interaction depends in large measure on the similarity between test and flanking stimuli. The stimulus consisted of a test T surrounded by four distracting flanking Ts, each randomly oriented. The task was to determine the orientation of the test T. The test and flanking Ts differed in contrast polarity, shape, depth, color, eye of origin, or contrast. When the target and flanks differed in contrast polarity, depth, or shape, performance improved markedly for all observers. A color difference enhanced the performance of most but not all observers. Eye-of-origin had no effect, that is, spatial interaction was identical when the target and flanks were presented to the same eye, or to opposite eyes. The role of stimulus duration in spatial interaction was examined in two additional experiments. In the first, the stimulus viewing duration was increased in order to allow the observer time to serially search for the test T. In the second experiment, a postmask was presented at the location of the test T. The results of these experiments showed that the influence of similarity was independent of stimulus duration and the postmask, and suggest that serial search does not play an important role in the spatial interaction effects reported here. The extent of spatial interaction is correlated with the ability to do parallel search.

Color Perception↗
PubMed2005

A standard model for foveal detection of spatial contrast.

The ModelFest data set was created to provide a public source of data to test and calibrate models of foveal spatial contrast detection. It consists of contrast thresholds for 43 foveal achromatic contrast stimuli collected from each of 16 observers. We have fit these data with a variety of simple models that include one of several contrast sensitivity functions, an oblique effect, a spatial sensitivity aperture, spatial frequency channels, and nonlinear Minkowski summation. While we are able to identify one model, with particular parameters, as providing the lowest overall residual error, we also note that the differences among several good-fitting models are small. We find a strong reciprocity between the size of the spatial aperture and the value of the summation exponent: both are effective means of limiting the extent of spatial summation. The results demonstrate the power of simple models to account for the visibility of a wide variety of spatial stimuli and suggest that special mechanisms to deal with special classes of stimuli are not needed. But the results also illustrate the limited power of even this large data set to distinguish among similar competing models. We identify one model as a possible standard, suitable for simple theoretical and applied predictions.

Contrast Sensitivity↗
PubMed2005

Spatial frequency sensitivity differences between adults of good and poor reading ability.

PURPOSE: To determine whether normal adults of good and poor reading ability exhibit different patterns of sensitivity to spatial frequency, as previously found between dyslexic and nondyslexic control subjects. METHODS: The visual acuity, spatial frequency sensitivity, and reading ability of 96 normal, nondyslexic adults was assessed. Participants were ranked according to reading ability. The top 50% were classified as good readers and the bottom 50% as poor readers. RESULTS: Despite no differences in visual acuity, good and poor readers showed different patterns of spatial frequency sensitivity. In particular, compared with good readers, poor readers showed reduced sensitivity to spatial frequencies between 2 and 6 cyc/deg, and no differences in sensitivity were found at lower or higher spatial frequencies. CONCLUSIONS: The findings indicate that spatial frequency sensitivity differences found previously between dyslexic and nondyslexic controls can extend to the normal (nondyslexic) adult population.

Adolescent↗