Harvey Babkoff

Linguistic processes in the two cerebral hemispheres: Implications for modularity VS interactionism

Three experiments are reported on lexical decision to target stimuli presented to the right or left visual field (RVF, LVF) following a variety of priming stimuli, words, incomplete sentences, and scrambled sentences. Lexical decision performance is always superior for stimuli presented to the RVF. Primes always facilitate the discrimination of words from nonword target stimuli presented to either visual field. However, when the prime is a sentence which is completed syntactically and semantically by a target word (normal, congruent sentence), the facilitation for RVF presented targets is significantly greater than for LVF targets. When the prime is either: (1) a single word, (2) a nonstructured (scrambled) sentence, or (3) a noncongruent-related sentence, the difference in facilitation between RVF and LVF presented targets is much smaller. These data are discussed with respect to (1) the nature of priming by sentences versus words, (2) language processing by the two hemispheres, and (3) modularity versus interactionism in language processing.

Hemispheric specialization or reading habits: Evidence from lexical decision research with Hebrew words and sentences.

This paper reports the results of a lexical decision-visual hemifield protocol using Hebrew words and nonwords. The lexical decision task was combined with sentence priming to examine the impact of hemispheric specialization and sentence length. The data are relevant to the Kirsner and Schwartz (1986) hypothesis that reading habits can explain the oft-reported right visual field (RVF) superiority in linguistic tasks. Both the target stimuli and the sentence primes were in Hebrew and 26 male right-handed native Hebrew speakers served as subjects. Hebrew is written and read from right to left. Therefore, according to the favorable foveal viewing explanation (Kirsner & Schwartz, 1986), there should have been no RVF superiority. The results indicated, however, highly significant RVF superiority. Furthermore, priming sentences, written in Hebrew, should direct the attention of the subject to the left visual field in expectation of the appearance of a target word. Nevertheless, the RVF superiority was even more significant when target stimuli were preceded by priming sentences. Both results indicated that reading habits and directed reading attention cannot explain RVF superiority in lexical decision.

Hemisphericity and Top-Down Processing of Language

This study investigated the impact of contextual prompts (priming words and sentences) on the classical finding of superior performance with right visual field stimulation in a lexical decision task. Subjects were presented with prompts of varying lengths (one, three, or six words). The prompts were followed by a target stimulus (word/nonword) to the right or the left visual field. Subjects were required to respond whether the target was a word or a nonword. The major purpose of the study was to determine the extent of right visual field (RVF) superiority, reflecting left hemisphere superiority, in language processing when target stimuli are preceded by semantically meaningful prompts. The results showed that increasing the number of priming words congruent with the target (creating a meaningful context) increased the advantage of the RVF over the left visual field presentation in lexical decision. Thus, even with an available strategy provided by congruent priming stimuli, RVF superiority in lexical decision is retained and even increased.

Monaural and binaural temporal integration of noise bursts.

SummaryA comparison was made between monaural and binaural temporal integration of noise bursts at threshold. The data indicate partial integration, with approximately a 6 dB decrease in threshold per decade increase in noise burst duration for both conditions of stimulation (i.e., parallel functions) for durations ranging from 4 to 256 msec. When thresholds in dB are plotted as a function of log duration, the linear component accounts for 99% of the data indicating no essential change in the partial integration functions up to at least 256 msec. The intercept difference between the monaural and binaural integration functions is 2.5 dB.

How sleep is related to fatigue.

OBJECTIVES It is evident that sleep patterns have direct effects on fatigue. However, the multidimensionality of fatigue may imply that complex patterns of relationships exist between fatigue and sleep characteristics. We aimed to study the correlations between fatigue and quantitative and qualitative sleep measurements, while taking into consideration depression and somatization which are known to affect both sleep and fatigue. We predicted that sleep quality, unattained by the effects of somatization and depression, would affect perceived fatigue more than the quantitative characteristics of sleep. DESIGN Employing a cross-sectional design, hypotheses were addressed using multiple hierarchical regression analyses according to established methods. METHODS Data were gathered from a targeted, randomly selected adult sample (N = 278) by means of subjective sleep reports, a mental health inventory, somatization inventory, several fatigue questionnaires and a demographic questionnaire. RESULTS Fatigue was significantly predicted by depression scores, somatization levels and subjective sleep quality, but not quantitative sleep characteristics such as sleep latency, nocturnal awakenings and early morning arousals. Depression levels were positively and significantly related to all aspects of fatigue except physical fatigue and fatigue that responds to rest and sleep. Physical fatigue was correlated with somatization, but not depression. CONCLUSIONS The data further our understanding of the multifaceted nature of human fatigue and underline the greater importance of perceived sleep quality, compared to other sleep characteristics, in predicting fatigue.

MONOTONIC AND RHYTHMIC INFLUENCES : A CHALLENGE FOR SLEEP DEPRIVATION RESEARCH

There are both monotonic and rhythmic factors in the patterns of change seen in physiological, psychological, and performance variables during sleep deprivation. These monotonic and rhythmic factors can be orthogonal, or they may interact with each other, with various task variables, or both. The importance of separating the rhythmic from the monotonic factors and of elucidating their interactions is discussed. Experimental methods and types of analysis appropriate to evaluating these factors are examined, with special emphasis on the complex demodulation time series analysis applied to group or individual subject data. The discussion is accompanied by data illustrations. It is suggested that sleep deprivation research should be designed so as to generate physiological and behavioral data that include information on both monotonic and rhythmic factors, the nature and extent of their interaction, and how they interrelate with systematically manipulated independent variables.

Mapping lateralization of click trains in younger and older populations

The main purpose of this study was to describe and compare lateralization of earphone-presented stimuli in younger and older individuals. Lateralization functions, relating perceived location to either interaural time differences (ITDs) or interaural level differences (ILDs) were determined for 78 subjects, aged 21-88 years, who responded by pressing one of nine keys to indicate the perceived location of the stimulus. All subjects were healthy, without any history of hearing loss or ear surgery and within the normal pure tone audiometric range for their age group. Interaural pure tone and click thresholds did not differ by more than 5 dB across ears. The ILD lateralization functions, ranging from 10 dB favoring the left ear to 10 dB favoring the right ear were linear. In contrast, the ITD lateralization functions were S-shaped with a clear linear component ranging from 750 micros favoring one ear to 750 micros favoring the other ear and with an asymptote from 750 micros to 1 ms. The same general shape of the ITD and ILD lateralization functions was found at all ages, but the linear slope of the ITD lateralization function became shallower with age. The ability to discriminate midline-located click trains (ITD and ILD=0) from ITD-lateralized click trains deteriorated with age, while the comparable ability to discriminate ILD-lateralized click trains did not change significantly with age. The data support two general conclusions. First there seems to be an overall reduction in the range of ITD-based lateralization due to aging. Second, there is a greater reduction in sensitivity due to aging in changes from the perceived midline position (ITD and ILD=0) when ITD is manipulated than when ILD is manipulated.

Effect of the diurnal rhythm and 24 h of sleep deprivation on dichotic temporal order judgment

The present study examined the impact of mild (24 h) sleep deprivation and of the circadian rhythm on auditory temporal resolution, measured by dichotic temporal order judgment (TOJ). The rationale for the present study was based on several areas of research. First, the ‘sleep‐based neuropsychological perspective’ hypothesis posits that sleep reduction initially impacts the functions associated with intact prefrontal cortical activity, e.g. language tasks. Secondly, recent studies indicate the importance of the role of auditory temporal resolution in speech comprehension. Thirdly, there is accumulating evidence of the involvement of prefrontal cortical structures in auditory temporal resolution. We hypothesized that mild to moderate sleep deprivation would affect dichotic TOJ negatively. The results showed that: (1) 24 h of sleep deprivation significantly reduced the overall level of accuracy in dichotic TOJ and increased dichotic TOJ threshold from 57.61 ms to 73.93 ms, a reduction in temporal resolution of 28.3%; (2) dichotic TOJ was subject to a small, but significant diurnal rhythm having a nadir in early to mid afternoon. As auditory temporal resolution of speech and non‐speech sounds seems to be dependent on intact functioning of the left inferior and left dorso‐lateral prefrontal cortex (PFC), these data strengthen the argument that even mild to moderate sleep deprivation can impact negatively on PFC‐dependent functions. Furthermore, based on these findings, we suggest that the deficit in auditory temporal resolution in individuals suffering from sleep loss may also affect language comprehension.

End Point of Lateralization for Dichotic Clicks

A series of experiments was undertaken to systematically study one aspect of binaural interaction for dichotically presented clicks—the end point of lateralization, which is referred to in this paper as the lag‐click threshold (Δt2). The results of experiments in which click parameters were manipulated are presented in Sec. III. These results indicate that the lag‐click threshold is decreased by an increase in the sensation level (SL) of both clicks, by an interaural intensity asymmetry favoring the lag crick, or by a decrease in the low‐frequency components of both clicks. The results of experiments in which the background‐noise parameters were manipulated appear in Sec. IV. As the SL of binaural broad‐band noise (125–8000 cps) is increased to 30 dB, the lag‐click threshold decreases; but as the noise level is increased further, the lag‐click threshold increases. The finding of a minimum point at 30 dB is related to the broad spectrum of the noise. One‐octave bandwidths of noise produce monotonic functio...

Deficits in temporal-order judgments in dyslexia: evidence from diotic stimuli differing spectrally and from dichotic stimuli differing only by perceived location.

The main debate concerning dyslexia focuses on the question of whether dyslexia is a language-specific disorder or a general nervous system dysfunction manifested in deficits of temporal processing. According to the temporal-order deficit hypothesis, dyslexia manifests difficulty in discriminating the temporal order of stimuli. Evidence has usually involved testing the ability to discriminate series of phonemes or pure tones whose components are separated by very short intervals. One of the difficulties in interpreting the data is the confound of changes in the spectrum with changes in temporal order. Two experiments are reported. In the first experiment, we verified the difficulty by adult dyslexics in judging the temporal order of two tones differing in frequency and presented diotically. The second experiment was designed to isolate temporal-order judgment (TOJ) from holistic frequency-based pattern discrimination processes. We tested temporal-order judgments with 15 ms duration tones of equal frequency presented dichotically (left-right, right-left) with ISI intervals ranging from 8 to 400 ms. Dichotic temporal threshold was significantly lower for adult normal readers than for the adult dyslexics. The results support the claim that adult dyslexics have difficulty in discriminating temporal order even when no spectral changes are involved.