Case effects in letter-name matching: A qualitative visual field difference

Subjects indicated whether or not two letters presented simultaneously to the left or right visual field had the same name. On same-name trials, reaction time was faster when both letters had the same case (physically identical, or PI, pairs) than when they were of different case (name identical, or NI, pairs) and reaction time was faster for left visual field presentations than for right visual field presentations. For left visual field presentations, the letter-case effect was as large on different-name trials as on same-name trials, indicating that the NI-PI difference was not simply a physical identity effect. In contrast, for right visual field presentations, the letter-case effect was restricted to same-name trials. These qualitatively different patterns for the two visual fields are discussed in terms of hypothesized consequences of cerebral hemisphere asymmetry for information processing in the normal brain

Case effects in letter-name matching: A partial replication

When same-case letter pairs are to be physically matched as “same” or “different,” reaction times (RTs) are generally shorter for “same” responses. The advantage in RT increases when such pairs are intermixed in blocks of trials also containing mixed-case pairs to be matched for name identity. These results have been interpreted as supportive of a two-code hypothesis of letter matching: In pure blocks of same-case pairs, a visual or physical code underlies letter matching, whereas in intermixed blocks, a phonetic or name code must be used for all “different” judgments. The theory predicts, however, that there should be little discrepancy in RT for same-case and mixed-case “different” pairs in intermixed blocks. Here a partial replication of Hellige and Webster (1981) is reported, showing that in fact there is a reliable discrepancy. This outcome poses problems for the two-code hypothesis, although it may be consistent with a “generation” hypothesis of letter matching

Categorization versus distance: Hemispheric differences for processing spatial information

It has been hypothesized that the brain computes two different kinds of spatial-relation representations: one used to assign a spatial relation to a category and the other used to specify metric distance with precision. The present visual half-field experiment offers support for this distinction by showing that the left and right cerebral hemispheres make more effective use of the categorization and metric distance representations, respectively. Furthermore, the inclusion of a bilateral stimulus presentation condition permits the computation of a reversed association that offers additional support for the distinction between two types of spatial-relation representation

Influence of noun imagery on speed of naming nouns

In an experiment on the influence of noun imagery on the speed of naming visually presented nouns, it was found that high-imagery nouns were named, on an average, 14 msec faster than low-imagery nouns. The difference, although small, was highly significant [F(l,14) = 10.04]. The magnitude of this effect was about one-third of that obtained when subjects were required to identify the grammaticality of phrases containing these same nouns, indicating that speed of encoding was probably a more important factor than speed of recognition in producing a noun imagery effect in speed of grammaticality judgments

The role of noun imagery in the speed of processing the grammaticality of adjective-noun phrases

This experiment investigated speed of processing the grammaticality of phrases consisting of the adjective one or two followed by a singular or plural noun. The subject\u27s task was to press one of two keys, depending upon whether the phrase was grammatically correct or incorrect. There were eight types of phrases, formed by the factorial combinations of singular or plural adjectives, singular or plural nouns, and high or low noun imagery. These served as within-subjects variables. Between-subjects variables were the factorial combinations of sex of subject, duration of stimulus phrase (.2 or 2.5 sec), and hand assigned to the correct-grammar key. A fourth between-subjects variable was whether or not the subject reported using an artificial phrase-scanning strategy to determine grammaticality. Correct grammar, singular noun form, high noun imagery, and reported use of the strategy all produced highly significant reductions in reaction times. Only 1% of the interactions were significant. A multistage serial processing model that could be based upon Sternberg\u27s additive factor paradigm or even Donders\u27 subtraction method was found to be highly successful in describing the results

Finite integer analysis of individual subject protocols during eyelid conditioning

Theios (1972) has proposed that during classical eyelid conditioning the conditioned response protocols of “voluntary” responders (Vs) will require an additional stage, relative to “conditioned” responders (Cs), to be adequately described. In a test of this hypothesis, individual subject protocols from eyelid conditioning experiments using both classical and avoidance modes of reinforcement were subjected to finite integer analysis (Theios, 1968). During both modes of reinforcement, a two-state Markov model was found to provide an adequate description of most individual protocols for both Cs and Vs. In addition, there were no indications that Vs give predominantly C-form conditioned responses at the beginning of an experimental session and switch to predominantly V-form conditioned responses later in the session. Both of these results indicate that Theios’ hypothesis is inaccurate at the level of the individual human subject

Effects of stimulus duration on processing lateralized faces

Observers indicated whether a single probe face presented to the left or right visual field was contained in a positive set of five male faces. In one task the distractor (i.e., negative) stimuli were also male faces, and in another task the distractor stimuli were female faces. For both tasks, reducing stimulus duration from 200 msec to 20 msec increased the percentage of errors, but for neither the percentage of errors nor the reaction time was there any stimulus duration × visual field interaction. In conjunction with earlier experiments using these same tasks, the results indicate that reducing stimulus duration does not have the same effect on visual laterality as does imposing a visual noise mask. These results pose problems for models predicting that a reduction in stimulus perceptibility per se produces a change in hemispheric asymmetry for face processing

Visual laterality for letter comparison: Effects of stimulus factors, response factors, and metacontrol

Right-handed subjects indicated whether two highly discriminable uppercase letters were the same or different. Letter pairs were projected to the left visual field/right hemisphere (LVF/RH) or the right visual field/left hemisphere (RVF/LH), or the same letter pair was presented to both visual fields simultaneously (bilateral trials). Laterality effects were not influenced by moderate blurring of the letters. However, on RVF/LH trials, reaction times were faster for same pairs than for different pairs. This effect was absent on LVF/RH trials, suggesting a qualitative difference in the mode of processing for the two unilateral trial types. The pattern of results on bilateral trials was identical to that obtained on RVF/LH trials. This suggests that on bilateral trials, the subjects employed the mode of processing characteristic of RVF/LH trials, perhaps indicating assertion of metacontrol by the left cerebral hemisphere

Hemispheric differences are found in the identification, but not the detection, of low versus high spatial frequencies

The processing of sine-wave gratings presented to the left and right visual fields was examined in four experiments. Subjects were required either to detect the presence of a grating (Experiments 1 and 2) or to identify the spatial frequency of a grating (Experiments 3 and 4). Orthogonally to this, the stimuli were presented either at threshold levels of contrast (Experiments 1 and 3) or at suprathreshold levels (Experiments 2 and 4). Visual field and spatial frequency interacted when the task required identification of spatial frequency, but not when it required only stimulus detection. Regardless of contrast level (threshold, suprathreshold), high-frequency gratings were identified more readily in the right visual field (left hemisphere), whereas low-frequency gratings showed no visual field difference (Experiment 3) or were identified more readily in the left visual field (right hemisphere) (Experiment 4). Thus, hemispheric asymmetries in the processing of spatial frequencies depend on the task. These results support Sergent\u27s (1982) spatial frequency hypothesis, but only when the computational demands of the task exceed those required for the simple detection of the stimuli