Directional scanning of remembered visual patterns

We report a set of experiments that helps to define the conditions under which mental image scanning may be used spontaneously for specific, practical purposes. Subjects were shown a dot pattern, followed by an arrow, and their task was to say whether the arrow was pointing at any of the previously seen dots. When no advance information was provided about the arrow's location, reaction time for correctly verifying that an arrow was pointing at a dot increased linearly with increasing arrow-dot distance, and the subjects almost always reported scanning a mental image in order to make their judgments. However, when a cue for the arrow's location was presented 2 sec beforehand, reaction time was uncorrelated with distance, and most of the subjects reported using an alternative strategy based on the determination in advance of correct directions from that location to the dots. When given only 1 sec of advance information about arrow location, most subjects reported using a combined image-scanning and advanced determination strategy, resulting in a reaction time function that increased only for the farthest distances. Because in each of these experiments instructions to form or to scan mental images were never given, these findings address the most common criticisms of the image-scanning paradigm.     

Hemispheric asymmetries in visual pattern processing in infancy

A right hemisphere advantage was observed in a previous study of 4- to 9-month old infants presented with a face discrimination task (de Schonen & Mathivet, 1990). The present study was designed to investigate pattern processing by the two hemispheres and the interhemispheric communication of this processing. Infants aged 4 to 9 months were tested with divided visual field presentations in one or two discrimination tasks. Under both task conditions, the infants had to discriminate between two patterns in which only two local components differed. Under one condition the components of the patterns were arranged so as to produce a face-like pattern. Under the other condition the same components were arranged into arbitrary patterns that were not "good form" patterns. No performance asymmetry was observed with the arbitrary patterns; whereas, a right hemisphere (RH) disadvantage was observed with the face-like patterns compared with both the RH performances on the arbitary patterns and the left hemisphere (LH) performances on the face-like patterns. These results show that the RH advantage for individual face recognition is not due to a general immaturity or inability of the LH in pattern processing at this period of development, nor to a more specific inability in a local mode of pattern processing. On the other hand, the RH does not completely lack local processing capacity, but is at a disadvantage when this local mode of processing has to be used with face-like (or good form) patterns. The interhemispheric communication of visual discrimination learning was tested by measuring learning transfer between the visual fields. Contrary to de Schonen and Bry's study (1987) on faceness recognition, no data in favor of interhemispheric communication were recorded in the present study.     

Information processing in imagination using nonverbalizable visual stimuli

In groups of 20 to 25, 146 undergraduates were tested as to their ability to mentally combine two shapes. They were to pick the correct choice from 5, 7, 9, 11, 13, or 15 alternatives. The shapes were previously proven to be effectively unverbalizable but recognizable and discriminable. Contrary to expectation, there was no negative decrement in performance with increasing numbers of incorrect alternatives.     

Subject variable effects in correlations between auditory and visual language processing asymmetries

The cross-modal correlations between auditory and visual language lateralization were examined as a function of the subject variables of handedness, sex, familial sinistrality, and handwriting posture. In this study, left-handers showed a significantly greater correlation between visual and auditory language processing asymmetries than right-handers, contradicting previous reports.     

Trade-offs in visual processing for stimuli near the hands

It is known that stimuli near the hands receive preferential processing. In the present study, we explored changes in early vision near the hands. Participants were more sensitive to low-spatial-frequency information and less sensitive to high-spatial-frequency information for stimuli presented close to the hands. This pattern suggests enhanced processing in the magnocellular visual pathway for such stimuli, and impaired processing in the parvocellular pathway. Consistent with that possibility, we found that the effects of hand proximity in several tasks were eliminated by illumination with red diffuse light—a manipulation known to impair magnocellular processing. These results help clarify how the hands affect vision.     

Attentional factors in visual field asymmetries.

Over the past 30 years, numerous studies have reported left/right asymmetries in visual field performance, with performance generally superior in the right visual field for verbal tasks and in the left visual field for spatial tasks. These asymmetries parallel those found in neurological studies of hemispheric specialization. Consequently, many investigators have concluded that visual hemifield differences are primarily a reflection of the functional differences between the two cerebral hemispheres. However, alternative explanations proposing that visual field effects are dependent on other factors such as inadequate fixation, eye movements during presentation, postexposural scanning, and attentional biases have been offered. The potential impact of each of these factors on visual field differences are reviewed and discussed. Evidence is provided suggesting that attention and hemispheric functional differences interact to produce the magnitude and direction of visual field differences.     

Successive vs simultaneous processing of superimposed visual stimuli

A visual analogue of Savin’s (1967) auditory task was used to examine preferred order of recall and order of recall accuracy for two pairs of visually superimposed digits. Savin (1967) and Rollins, Everson, and Schurman (1972) found that Ss preferred to recall simultaneous auditory information in successive order, even though the information was presented over a single channel. In the present experiments, Ss were found to prefer strongly to recall visual information in simultaneous order. On the other hand, the results of Rollins et al (1972), that Ss are equally accurate when forced to recall simultaneous auditory information in either the preferred or nonpreferred mode, were replicated for this visual task. The results of these experiments, together with the experiment reported by Rollins et al (1972), indicate that verbal information is processed differently by these two sensory systems.     

Facilitated processing of visual stimuli associated with the body

Recent work on tactile perception has revealed enhanced tactile acuity and speeded spatial-choice reaction times (RTs) when viewing the stimulated body site as opposed to viewing a neutral object. Here we examine whether this body-view enhancement effect extends to visual targets. Participants performed a speeded spatial discrimination between two lights attached either to their own left index finger or to a wooden finger-shaped object, making a simple distal--proximal decision. We filmed either the finger-mounted or the object-mounted lights in separate experimental blocks and the live scene was projected onto a screen in front of the participants. Thus, participants responded to identical visual targets varying only in their context: on the body or not. Results revealed a large performance advantage for the finger-mounted stimuli: reaction times were substantially reduced, while discrimination accuracy was unaffected. With this finding we address concerns associated with previous work on the processing of stimuli attributed to the self and extend the finding of a performance advantage for such stimuli to vision.     

Individual differences in adult foveal visual asymmetries.

The existence and nature of asymmetries in the recognition of elements of a visually presented array have been topics of dispute. In the present study, 32 adults responded to a single vertical or horizontal bar embedded in one circle of a 5 times 7 array of circles by touching a plate corresponding to the orientation of the bar. Two thirds of the subjects were left superior, while one third were right superior. Performance was in general top superior and decreased with increasing distance from the center. Possible explanations for these asymmetries are examined in terms of sequential processing, acuity dominance, hemispheric specialization, and selective attention.     

Hemispheric asymmetries in visual word-form processing: progress, conflict, and evaluating theories

The ubiquitous left-hemisphere advantage in visual word processing can be accounted for in different ways. Competing theories have been tested recently using cAsE-aLtErNaTiNg words to investigate boundary conditions for the typical effect. We briefly summarize this research and examine the disagreements and commonalities across the theoretical perspectives. This work may provide a good example why a multi-level, multi-method, and multi-paradigm approach holds the greatest promise for rapid theoretical progress.     

Evoked potential and visual half-field evidence for task-dependent cerebral asymmetries in congenitally deaf adults

Evoked potentials to laterally presented stimuli were collected from left and right tempero-parietal sites during performance of two visual half-field tasks, lexical decision, and line orientation discrimination. Reaction time and accuracy data were simultaneously collected. The behavioral data indicated the development of a right field advantage for the lexical decision task as a function of practice. A principal components analysis revealed three independent evoked potential components which displayed task-dependent hemispheric asymmetries. Multiple regression analyses revealed that visual half-field asymmetries in response accuracy were closely related to hemispheric asymmetries on several independent evoked response components. Subject's scores on independent tests of verbal reasoning and spatial relations were also found to be closely related to hemispheric asymmetry on several independent evoked response components. These data support a multidimensional concept of cerebral specialization. They also suggest that visual field asymmetries reflect the confluence of several underlying processes which have independent lateralization distributions across the population. In general, the results underscore the need for further research on the nature of the relationship between cerebral and perceptual asymmetries.     

On the processing of simple visual and auditory stimuli at distinct levels

Two RT studies explored the possibility that identification of a single stimulus can take place through more than one perceptual route. In the first experiment, mean RT to color was systematically changed by varying type of catch stimulus. In the second experiment, the form of the RT distribution to a tone was changed by varying type of catch stimulus. Considerations of distribution means and shapes led to the conclusion that detection and discrimination are two of the alternative levels of perceptual processing which can be evoked in rapid identification of these stimuli.     

An examination of relationship between subliminal perception, visual information processing, levels of processing, and hemispheric asymmetries

A sublimiinal letter was exposed to the left or right hemisphere for either 15 or 30 msec. Subjective guesses were more accurate for visuo-spatial positional recognition made to presentations in the right hemisphere whereas verbal recognition was more accurate to presentations in the left hemisphere. The 30-msec. exposure increased the accuracy of the guesses. These findings were discussed in terms of differential triggering mechanisms for levels of hemispheric processing.     

Death anxiety and visual oculomotor processing of arousing stimuli in a free view setting

The main goal of this study was to determine how death anxiety (DA) affects visual processing when confronted with arousing stimuli. A total of 26 males and females were primed with either DA or a neutral primer and were given a free view/free choice task where eye movement was measured using an eye tracker. The goal was to identify measurable/observable indicators of whether the subjects were under the influence of DA during the free view. We conducted an eye tracking study because this is an area where we believe it is possible to find observable indicators. Ultimately, we observed some changes in the visual behavior, such as a prolonged average latency, altered sensitivity to the repetition of stimuli, longer fixations, less time in saccadic activity, and fewer classifications related to focal and ambient processing, which appear to occur under the influence of DA when the subjects are confronted with arousing stimuli.     

The costs and benefits of processing emotional stimuli during rapid serial visual presentation

Using a dual-target identification task during rapid serial visual presentation (RSVP), we examined facilitation and interference effects exerted by emotional stimuli. Emotionally arousing first targets (T1s) were encoded with higher accuracy than neutral T1s. At the same time, identification of a second neutral target (T2) was impaired reflecting a failure of disengaging attention from arousing T1s. Similar interference was triggered by arousing filler stimuli that were not voluntarily searched for in the RSVP stream (Experiment 2). In Experiment 3, we showed that interference is reduced (though facilitation for arousing T1s is maintained) when the second task itself involves variations in emotional arousal. Vice versa, when arousal associated with the T2 stimulus was predictable, interference recurred (Experiment 4). Our findings indicate that the perceived emotional intensity of a stimulus is a determinant of successful identification during RSVP: Encoding of arousing stimuli is reliably facilitated. Interference effects with subsequent processing arise independently and are strongly modulated by the overall task context and specific processing strategies.     

Facilitation and disruption of lateralized syllable processing by unattended stimuli in the opposite visual field

The influence of lateralized unattended stimuli on the processing of attended stimuli in the opposite visual field can shed light on the nature of information that is transferred between hemispheres. On a cued bilateral task, participants tried to identify a syllable in the attended visual field, which elicits a left hemisphere (LH) advantage and different processing strategies by the two hemispheres. The same or a different syllable or a neutral stimulus appeared in the unattended field. Transmission of unattended syllable codes between hemispheres is symmetric, as revealed by equal interference for the two visual fields. The LH is more accurate than the RH in encoding unattended syllables, as indicated by facilitation in the left but not right visual field and a greater frequency of identifiable intrusions into the left than right field. However, asymmetric encoding strategies are different for attended and unattended syllables.     

Perceiver and poser asymmetries in processing facial emotion

This study examined both perceiver and poser asymmetries in processing facial emotion. Posers were left brain-damaged (LBD), right brain-damaged (RBD), and normal control (NC) right-handed males videotaped while expressing happiness and anger. Perceivers rated the facial expressions for asymmetry in original and reversed orientations. Overall, expressions viewed in the reversed orientation were rated as more left-sided than in the original orientation. In the reversed orientation, the more extensive left hemiface of the NCs and LBDs fell in the perceiver's left hemispace. This finding is consistent with previous research demonstrating a left hemispace bias for free-field viewing of emotional faces. Expressions were produced significantly more intensely on the left than the right hemiface by NCs and LBDs; expressions of RBDs were not significantly lateralized.     

Functional hemispheric asymmetries of global/local processing mirrored by the steady-state visual evoked potential

While hemispheric differences in global/local processing have been reported by various studies, it is still under dispute at which processing stage they occur. Primarily, it was assumed that these asymmetries originate from an early perceptual stage. Instead, the content-level binding theory (Hübner & Volberg, 2005) suggests that the hemispheres differ at a later stage at which the stimulus information is bound to its respective level. The present study tested this assumption by means of steady-state evoked potentials (SSVEPs). In particular, we presented hierarchical letters flickering at 12 Hz while participants categorised the letters at a pre- cued level (global or local). The information at the two levels could be congruent or incongruent with respect to the required response. Since content-binding is only necessary if there is a response conflict, asymmetric hemispheric processing should be observed only for incongruent stimuli. Indeed, our results show that the cue and congruent stimuli elicited equal SSVEP global/local effects in both hemispheres. In contrast, incongruent stimuli elicited lower SSVEP amplitudes for a local than for a global target level at left posterior electrodes, whereas a reversed pattern was seen at right hemispheric electrodes. These findings provide further evidence for a level-specific hemispheric advantage with respect to content-level binding. Moreover, the fact that the SSVEP is sensitive to these processes offers the possibility to separately track global and local processing by presenting both level contents with different frequencies.