Asymmetry of visual interference

This research studies lateral interference among items in the visual field under conditions in which central cognitive factors such as attention and memory limitations are eliminated or controlled for. Under these conditions lateral masking is still found, and it is still asymmetrical (peripheral items interfere with recognition of central items more than central with peripheral). These experiments therefore add to the evidence that both lateral interference and the asymmetry of interference have a component that does not result from cognitive strategies. The experiments also add to the evidence that the asymmetry effect at the sensory level can be attributed to the falloff in acuity from the center to the periphery of the retina, since the mean eccentricity of the target-mask cluster is more peripheral with a peripheral mask than with a central mask. The hypothesis is advanced that the asymmetry effect, as well as lateral interference itself, at the sensory level results from the grouping of target and mask into a single Gestalt-like configuration. The final experiment in the series supports this hypothesis     

The growth of the effective visual field from birth to seven weeks

Visual orientation toward a peripheral stimulus by newborns and 7-week-old infants was examined with both a central stimulus present and absent. The presence of the central stimulus narrowed but did not eliminate peripheral responding. No age change was found when a central stimulus was present. However, older infants exhibited greater peripheral responding than newborns when the central stimulus was absent. The neonate appears to exercise internal control over his sampling of the stimulus array rather than being passively captured by it.     

The neural basis of the right visual field advantage in reading: an MEG analysis using virtual electrodes

Right-handed participants respond more quickly and more accurately to written words presented in the right visual field (RVF) than in the left visual field (LVF). Previous attempts to identify the neural basis of the RVF advantage have had limited success. Experiment 1 was a behavioral study of lateralized word naming which established that the words later used in Experiment 2 showed a reliable RVF advantage which persisted over multiple repetitions. In Experiment 2, the same words were interleaved with scrambled words and presented in the LVF and RVF to right-handed participants seated in an MEG scanner. Participants read the real words silently and responded "pattern" covertly to the scrambled words. A beamformer analysis created statistical maps of changes in oscillatory power within the brain. Those whole-brain maps revealed activation of the reading network by both LVF and RVF words. Virtual electrode analyses used the same beamforming method to reconstruct the responses to real and scrambled words in three regions of interest in both hemispheres. The middle occipital gyri showed faster and stronger responses to contralateral than to ipsilateral stimuli, with evidence of asymmetric channeling of information into the left hemisphere. The left mid fusiform gyrus at the site of the 'visual word form area' responded more strongly to RVF than to LVF words. Activity in speech-motor cortex was lateralized to the left hemisphere, and stronger to RVF than LVF words, which is interpreted as representing the proximal cause of the RVF advantage for naming written words.     

Direct visual access in reading for meaning

Two experiments examined whether phonological receding is an obligatory stage in reading for meaning or whether direct access to a word's semantic representation is the general rule. The first study demonstrated that the time to make a semantic decision about a pair of words was much more delayed by misspelling than was the time to make a phonological one. The second study investigated the effect of varying the syllabic length of a word on reaction time in a category decision task. While reaction time varied with the semantic difficulty of the category decision, it generally proved invariant with respect to syllabic length. It is argued that reading for meaning generally uses a direct route from visual form to semantic representation.     

Measurement of the visual field

There is increasing evidence that concurrent visual and nonvisual tasks not only reduce the size but also result in systematic deformation of the visual field. Given such complex changes in the visual field, appropriate representation and measurement of its shape is all important. Shape measures utilized by researchers and reported in the literature should also be sufficiently standardized to allow comparison of results across experiments.     

Brightness perception in the visual field

Summary Apparent brightness was measured at different positions in the visual field for scotopic, mesopic, and photopic adaptation levels by means of a magnitude estimation technique. Apparent brightness of targets with a given luminance remained rather constant throughout the visual field for the mesopic and photopic adaptation level; for the scotopic adaptation level targets in the foveal and perifoveal area had to be more intense in order to appear as bright as targets in the far periphery (beyond 20° eccentricity). For the photopic range, two brightness power functions with different exponents were obtained for the luminance range from 1 to 100 mL at each eccentricity. The exponent for the range from 1 to 10 mL is considerably greater than the exponent beyond 10 mL, and appears to increase with increasing eccentricity.The experiments described in this paper were partly supported by Deutsche Forschungsgemeinschaft and SFB 50-C 6.     

The span of the effective stimulus during a fixation in reading

A computer-based eye-movement controlled, display system was developed for the study of perceptual processes in reading. A study was conducted to identify the region from which skilled readers pick up various types of visual information during a fixation while reading. This study involved making display changes, based on eye position, in the text pattern as the subject was in the act of reading from it, and then examining the effects these changes produced on eye behavior. The results indicated that the subjects acquired word-length pattern information at least 12 to 15 character positions to the right of the fixation point, and that this information primarily influenced saccade lengths. Specific letter- and word-shape information were acquired no further than 10 character positions to the right of the fixation point.     

Allocation of attention in the visual field

This research investigated whether attentional resources can be simultaneously allocated to several locations in a visual display, whether the mode of processing (serial or parallel) can be switched within a trial, and the nature of the costs when attentional resources are concentrated on an invalid location. Subjects were required to determine which of two target letters was present in eight-letter circular displays. In precue conditions, a primary and a secondary target location were designated 150 ms before target onset by an indicator that varied in validity. In the control conditions no cue was provided. A second experiment verified several assumptions that had been made in interpreting the data of Experiment 1. Modifications in Jonides' (1983) two-process model were suggested in terms of a zoom lens model of attentional resources. Instead of two alternative processing modes, attentional resources are conceived as capable of distribution over the visual field, but with low resolving power, or as continuously constricting to small portions of the visual field with a concomitant increase in processing power.     

Vertical perceptual span and the processing of visual signals in reading

A previous study by Pollatsek et al. ( 1993 ) claims that the perceptual span in reading is restricted to the fixated line, i.e. readers typically focus their visual attention on the line of text being read. The present study investigated whether readers make use of content structure signals (paragraph indentations and topic headings) present several lines away from the currently fixated line. We reasoned that as these signals are low-resolution visual objects (as opposed to letter and word identity), readers may attend to them even if they are located some distance away from the fixated line. Participants read a hierarchically organized multi-topic expository text containing structure signals in either a normal condition or a window condition, where the text disappeared above and below a vertical 3° gaze-contingent region. After reading, participants were asked to produce a written recall of the text. The results showed that the overall reading rate was not affected by the window. Nevertheless, the headings were reread more in the normal condition than in the window one. In addition, more topics were recalled in the normal than in the window condition. We interpret the results as indicating that the readers visually attend to useful text layout features while considering bigger units than single text lines. The perception of topic headings located away from the fixated line may favour long-range regressions towards them, which in turn may favour text comprehension. This claim is consistent with previous studies that showed that look-back fixations to headings are performed with an integrative intent.     

A visual display system for reading and visual perception research

The selection of a computer visual display system suitable for word recognition and reading research is described. The software character generation routines permit flexible definition of character sets. The display software permits control of size scaling and point density of characters being displayed as well as control over the temporal microstructure of presenting and refreshing the displayed text.     

Development of the functional visual field

Andries Sanders' dissertation examined selective mechanisms in the functional visual field, and much of his work since has been concerned with the stages that underlie visual information processing particularly while making saccades. We argue that the study of orienting in the functional visual field is timely because it deals with the relation of covert attention shifts, eye movements and head movements to their underlying neurology. In our paper we develop a method to study learning of sequences at all ages from infants to adults. Our studies focus on how learning influences anticipatory eye movements. We examined the learning of unambiguous and context dependent sequences by 4-, 10-, and 18-month-old infants and undergraduates. We found clear learning of unambiguous sequences at 4 months, but learning of context dependent associations was found only in 18-month-olds and in adults. We hypothesize that the learning of unambiguous sequences by 4-month-olds reflects maturation of a basal ganglia-parietal circuit related to adult implicit learning, while the learning of context dependent sequences requires development of frontal structures underlying more general attentional abilities.     

Orientation sensitivity in the peripheral visual field

Orientation sensitivity in the peripheral visual field has been tested in two tasks: (a) setting horizontal the orientation of a grating at various retinal eccentricities, and (b) matching the orientation of a peripherally viewed grating as close as possible to an oblique reference viewed foveally. Both performances fall off with increasing retinal eccentricity. Magnification of the stimulus optimizes peripheral performance. Peripheral performance, optimized by magnification, varies with retinal eccentricity. It approaches, but does not reach, the foveal value (tested by the same method) at 10 deg of eccentricity, and is much lower at 20 and 30 deg of eccentricity.     

Asymmetry in infant hemispheric readiness after exposure to a visual stimulus

This experiment assessed whether prior exposure to one visual stimulus could result in differential hemispheric responsiveness to a subsequent visual stimulus. The latency of saccadic orientation to a star‐shaped stimulus in the left or right visual field was assessed for 24 infants (mean age 22 weeks, SD 4.5) after exposure to either an upright or inverted facial pattern in the central visual field. The response to the lateral stimulus was equivalent in either visual field after exposure to the inverted facial pattern, but was significantly slower (p = 0.043) in the LVF (RH) than the RVF (LH) following presentation of the upright facial pattern. The outcome confirms that the processing of one visual stimulus may lead to differential hemispheric readiness to engage with a subsequent visual stimulus.