Word Recognition

(Editor:   Jean Mandernach)

Introduction

Hemispheric specialization refers to the differential functioning of each hemisphere, or lateral half, of the brain. Despite considerable overlap in the processing functions of both hemispheres, the left hemisphere primarily governs language and verbal abilities, whereas the right hemisphere excels at nonverbal and spatial tasks (Springer & Deutsch, 1989).

The divided visual field technique has advanced knowledge of hemispheric specialization in language and lexical decision-making (Barton, Goodglass, & Shai, 1965). Using the divided visual field technique, researchers tachistoscopically present words either to the left or to the right visual field of a participant. Researchers then measure how long a word must appear in order for the participant to consciously recognize it. Findings indicate that participants recognize words processed in the left hemisphere faster and more accurately than words processed in the right hemisphere; psychologists attribute this difference to the superior language and verbal abilities found in the left hemisphere (Barton, Goodglass, & Shai, 1965; Bryden & Ramey, 1963; Hamers & Lambert, 1977; Kershner & Jeng, 1972).

The value of the divided visual field technique in investigating hemispheric specialization lies in its unique design that allows information to be selectively presented either to the left or to the right hemisphere. In the divided visual field technique, participants focus on a central fixation point that is equal distance from both eyes. Words (vertically oriented) are then flashed to either the right or left of the fixation point. The flashed words appear long enough to be recognized but too quickly to allow eye movement. Because people process visual information contralaterally, words presented to the right visual hemifield are processed in the left hemisphere and words presented to the left visual hemifield are processed in the right hemisphere.

To understand this phenomenon, one must examine how visual information is routed and processed. Although all visual information is captured by both eyes, the rounded shape of the retina dictates that images appear primarily on one half of the retina, either the temporal half or the nasal half. Figure 1 illustrates the retinal divisions.

picture of eye
Figure 1

As such, the temporal retina of one eye and the nasal retina of the other eye see almost identical visual fields. Dividing the visual field at the center, the right hemifield sends signals to the left temporal retina and the right nasal retina; the opposite is true for the left hemifield. Due to the contralateral functioning of the brain, information from the nasal retinas crosses the optic chiasm to be processed in the opposite hemisphere (information from the temporal retinas does not need to cross as it already perceives the opposite side). The routing of visual information is illustrated in Figure 2.

full figure of eye in relationship to brain
Figure 2

This visual system structure results in "processing priority" for one hemisphere over the other when information is selectively presented to only one visual hemifield (this priority would not be present for information presented at the midline where it would be routed to both hemispheres simultaneously).

Research on hemispheric specialization has also examined the interaction of other variables, such as laterality and gender, on lexical processing. Findings indicate that right-handed individuals show strong left hemisphere dominance for processing verbal and language information, whereas left-handed individuals use more bilateral processing (Knecht, Dräger, Deppe, Bobe, Lohmann, Flöel, Ringelstein & Henningsen, 2000). In addition, females on average are less lateralized than males (see Hiscock, Israelian, Inch, Jacek, & Hiscock-Kalil, 1995 for a review) and thus show less left hemisphere dominance in language processing.

Design

This study involves a series of word recognition trials in which participants are flashed a word either in the left or in the right hemifield and then identify the presented word. In each trial, participants fixate their eyes on a pulsating point (plus sign) that appears in the middle of the screen. Vertically oriented words are then flashed one-at-a-time either to the right or to the left of the center point. Following each word presentation, participants identify the word by typing it in a text entry box. Correctly identified words are removed from the presentation sequence; words not correctly identified remain in the presentation sequence (appearing for a longer period of time on subsequent trials). This presentation sequence continues until the participant has identified all words correctly.

To assure central fixation and to prevent anticipation of the word presentation, the pulsating point stays on the screen for a random delay of 3 to 5 seconds prior to word presentation. The stimuli words for this task are 16 5-letter English words, all of which are common but relatively low in frequency. Half of the words are presented in the right visual field and half in the left visual field. The order of word presentation as well their left-right presentation assignment is random. Display times begin at .09 seconds for the initial presentation of a word and increase at 10 millisecond increments until the participant recognizes the word.

Performance is measured as the minimum presentation display time required for an individual to correctly identify the word. The within-subject variable is the visual field in which a word is presented; between-subject variables are handedness and gender.

Data Download, Format and Analyses

Performance is measured as the minimum presentation display time required for an individual to correctly identify the word. The within-subject variable is the visual field in which a word is presented; between-subject variables are handedness and gender.

Sample data appears below:

Sample data image from the word recognition Data experiment
Figure 1

The first six columns provide demographic and classification data (participant ID number, class ID number, gender, age, hand preference, and study completion date). The last two columns indicate the mean recognition time required for words presented to each visual field (RIGHT is the average amount of time for correct recognition of words presented in the right visual field; LEFT is the average amount of time for correct recognition of words presented in the left visual field).

Appropriate analyses include a paired samples t-test or repeated-measures one-way ANOVA to compare mean recognition times for words presented to the right and left visual fields. It is hypothesized that participants will recognize words presented to the right visual field (processed by the left hemisphere) faster than words presented to the left visual field (processed by the right hemisphere).

Additional between-subject analyses can include examining the effect of laterality and gender on lexical processing.

  • Laterality - An ANOVA (in which visual field is a within-subjects factor and handedness is a between-subject factor) will test the role of handedness on hemisphere dominance of language processing. A reasonable hypothesis is that left-handed participants will show significantly smaller left-right mean differences than will right-handed participants due to the increased bilateral processing that left-dominant individuals use.
  • Gender - Because females tend to be less lateralized than males, a logical hypothesis is that they will show a smaller left-right mean difference than males. The interaction term of an ANOVA that treats visual field as a within-subjects factor and gender as a between-subjects factor will reveal the level of significance of the difference.

If the data set is large enough, the effect of these variables can be extended even further using MANOVA to examine the interaction between laterality and gender on word recognition. A plausible hypothesis is that left-handed females will show the smallest left-right difference in lexical processing, whereas right-handed males will show the largest.

Applications and Extensions

Research on hemispheric specialization in lateralized recognition tasks has examined a range of factors that may influence or interact with the left-right dominance of particular tasks. Some of the key variables that researchers investigated include: instruction (i.e., verbal or imagery) (Cormier & Jackson, 1995), stress (Gruzelier & Phelan, 1991), psychopathology (Hare & Jutai, 1988), non-words (Jordan, Redwood, & Patching, 2003), emotional content (Atchley, Ilardi & Enloe, 2003) and ambiguity (Faust & Gernsbacher, 1996).

The divided visual field technique is a valuable strategy for examining hemispheric specialization across a range of abilities. In addition to its use in research on lexical processing, the divided visual field technique has been effectively utilized in research on abilities such as facial affect perception (Ley & Bryden, 1979), perception of emotion (Compton, Banich, Mohanty, Milham, Herrington, Miller, Scalf, Webb, & Heller, 2003) and attachment (Cohen & Shaver, 2004).

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