Local-global interference is modulated by age, sex and anterior corpus callosum size

Abstract

To identify attentional and neural mechanisms affecting global and local feature extraction, we devised a global-local hierarchical letter paradigm to test the hypothesis that aging reduces functional cerebral lateralization through corpus callosum (CC) degradation. Participants (37 men and women, 26-79 years) performed a task requiring global, local, or global+local attention and underwent structural MRI for CC measurement. Although reaction time (RT) slowed with age, all participants had faster RTs to local than global targets. This local precedence effect together with greater interference from incongruent local information and greater response conflict from local targets each correlated with older age and smaller callosal genu (anterior) areas. These findings support the hypothesis that the CC mediates lateralized local-global processes by inhibition of task-irrelevant information under selective attention conditions. Further, with advancing age smaller genu size leads to less robust inhibition, thereby reducing cerebral lateralization and permitting interference to influence processing. Sex was an additional modifier of interference, in that callosum-interference relationships were evident in women but not in men. Regardless of age, smaller splenium (posterior) areas correlated with less response facilitation from repetition priming of global targets in men, but with greater response facilitation from repetition priming of local targets in women. Our data indicate the following dissociation: anterior callosal structure was associated with inhibitory processes (i.e., interference from incongruency and response conflict), which are vulnerable to the effects of age and sex, whereas posterior callosal structure was associated with facilitation processes from repetition priming dependent on sex and independent of age.

Figure 1

Correlations between age and the mean area size of the subregions genu (r = −.56, p < .0001), body (r = −.32, p = .05), and splenium (r = −.26, n.s.) of the corpus callosum, the thick band of white matter fibers connecting the two cerebral hemispheres (left panel). Comparison of callosal area (genu, body, splenium) between women and men (right panel). CC-area are expressed as Z-scores corrected for intracranial volume (IVC), for women and men.

Figure 2. Precedence effects

Model of parallel processing with global letters preferentially processed in the right cerebral hemisphere and local letters in the left cerebral hemisphere (upper middle panel). Mean reaction times (RT) and standard errors (SE) as a function of attention condition (selective vs. divided). Left and right panels: Examples of stimuli (global vs. local targets) used for the calculation of the precedence effects under (a) selective attention (left panel) and (b) divided attention conditions (right panel). Green circles: attention to local features; red circles: attention to global features. Gg: Global attention block/global target; Ll: Local attention block/local target; Bg: Both (global+local) attention block/global target; Bl: Both (global+local) attention block/local target. Correlations between the precedence effect (difference RTs to global minus local features) and age (selective attention: r = .32, p = .05; divided attention: r = −.05, ns) and the size of the genu area of the corpus callosum (CC) selective attention: r = −.34, p = .03; divided attention: r = −.21, ns).

Figure 3. Interference, response conflict and facilitation effects

Model of interhemispheric local and global feature processing. Examples of the stimuli used to calculate (a) interference effects, (b) response conflict, and (c) response facilitation effects from targets at the unattended spatial scale. Mean difference reaction times and standard errors (SE) as a function of congruity between targets at either level (a), or the presence of unattended targets alone (b) or together with attended targets (c). Gg: Global attention block/global target; Gl: Global attention block/local target; Gb: Global attention block/global+local target; Gn: Global attention block/no target; Ll: Local attention block/local target; Lg: Local attention block/global target; Lb: Local attention block/global+local target; Ln: Local attention block/no target. Correlations between genu area of the corpus callosum (CC) and interference from incongruency (left down) (r = −.48, p = .003), genu area and response conflict (middle down) (r = −.43, p = .008) and age and response conflict (right down) (r = .31, p = .06).

Figure 4. Repetition priming and switching effects

Examples of the stimuli used to calculate repetition priming (left) and switching effects (right) (a) from local to global and (b) from global to local, under divided attention conditions. Mean reaction times and standard errors (SE) of the two consecutive trials (n-1, n) for global and local repetition, and for global and local switch are displayed. Repetition and switch effects, i.e., mean difference reaction times and SE between n-1 and n trials. Correlation between the callosal splenium area and global (left panel) (men: r = −.53, p < .02; women r = −.00, ns) and local (right panel) (men: r = −.02, ns; women r = −.50, p = .035) repetition priming calculated as mean RT difference between RTs between n-1 and n trials for global and for local target repetitions.

Figure 5

Design of the local-global paradigm: 3 attention blocks (1. Attend the global level, 2. Attend the local level, 3. Attend both levels) with 4 randomly intermixed conditions (global targets, local targets, both global and local targets, neither global nor local targets) were repeatedly presented. Target letters were Es and Ts, non-target letters Fs and Ls. Participants answered the question: “Is there an E or a T?” by pressing a Yes key for targets (E and T) and a No key for non-targets (F and L) at the attended level(s).