Inhibition of Return Generated by Voluntary Saccades is Independent of Attentional Momentum

Age differences in inhibitory and working memory functioning: limited evidence of system interactions

Debate persists regarding the nature of age-related deficits in inhibition, and whether inhibitory functioning depends on working memory systems. The current research aimed to measure age-related differences in inhibition and working memory, characterize the relationship between inhibitory functions and working memory performance, and determine how these relationships are affected by age. Toward these ends, we measured performance on a range of established paradigms in 60 young adults (18-30 years) and 60 older adults (60-88 years). Our findings support age-related increases in reflexive inhibition (based on the fixation offset effect and inhibition of return) and age-related decrements in volitional inhibition (based on several paradigms: antisaccade, Stroop, flanker, and Simon). This evidence of stronger reflexive inhibition combined with weaker volitional inhibition suggests that age-related deterioration of cortical structures may allow subcortical structures to operate less controlled. Regarding working memory, older adults had lower backward digit scores and lower forward and backward spatial scores. However, of the 32 analyses (16 in each age group) that tested for dependence of inhibitory functioning on working memory functioning, only one (in young adults) indicated that inhibition performance significantly depended on working memory performance. These results indicate that inhibition and working memory function largely independently in both age groups, and age-related working memory difficulties cannot account for age-related declines in inhibitory control.

Saccade latency indexes exogenous and endogenous object-based attention

Classic studies of object-based attention have utilized keypress responses as the main dependent measure. However, people typically make saccades to fixate important objects. Recent work has shown that attention may act differently when it is deployed covertly versus in advance of a saccade. We further investigated the link between saccades and attention by examining whether object-based effects can be observed for saccades. We adapted the classical double-rectangle cueing paradigm of Egly, Driver, and Rafal (1994), and measured both the first saccade latency and the keypress reaction time (RT) to a target that appeared at the end of one of the two rectangles. Our results showed that saccade latencies exhibited higher sensitivity than did RTs for detecting effects of attention. We also assessed the generality of the attention effects by testing three types of cues: hybrid (predictive and peripheral), exogenous (nonpredictive and peripheral), and endogenous (predictive and central). We found that both RTs and saccade latencies exhibited effects of both space-based and object-based attentional selection. However, saccade latencies showed a more robust attentional modulation than RTs. For the exogenous cues, we observed a spatial inhibition of return along with an object-based effect, implying that object-based attention is independent of space-based attention. Overall, our results revealed an oculomotor correlate of object-based attention, suggesting that, in addition to spatial priority, object-level priority also affects saccade planning.

Further evidence against a momentum explanation for IOR

Reaction times to targets presented in the same location as a preceding cue are greater than those to targets presented opposite the cued location. This observation can be explained as a result of inhibition at the attended location (IOR), or as facilitation at the location opposite the cue (opposite facilitation effect or OFE). Past research has demonstrated that IOR is observed reliably, whereas OFE is observed only occasionally. The present series of four experiments allows us to determine whether or not OFE can be explained by eye movements as suggested by previous authors. Participants' eye movements were monitored as they were presented with an array of four placeholders aligned with the four cardinal axes. Exogenous cues and targets were presented successively. Participants (N=37) completed either: i.) cue-manual and cue-saccade experiments, ignoring the cue and then responding with a keypress or saccade, respectively, or ii.) manual-manual and saccade-saccade experiments, responding to both the cue and the target with a keypress or saccade respectively. Results demonstrated a reliable IOR effect in each of the four experiments (reaction time greater for same versus adjacent and opposite cue-target trials). None of the four experiments demonstrated evidence of an OFE (reaction times were not significantly lower for opposite versus adjacent cue-target trials). These results are inconsistent with a momentum-based account of cue-target task performance, and furthermore suggest that the OFE cannot be attributed to occasional eye movements to the cue and/or target in previous studies.

Spatial interactions between successive eye and arm movements: signal type matters

Spatial interactions between consecutive movements are often attributed to inhibition of return (IOR), a phenomenon in which responses to previously signalled locations are slower than responses to unsignalled locations. In two experiments using peripheral target signals offset by 0°, 90°, or 180°, we show that consecutive saccadic (Experiment 1) and reaching (Experiment 3) responses exhibit a monotonic pattern of reaction times consistent with the currently established spatial distribution of IOR. In contrast, in two experiments with central target signals (i.e., arrowheads pointing at target locations), we find a non-monotonic pattern of reaction times for saccades (Experiment 2) and reaching movements (Experiment 4). The difference in the patterns of results observed demonstrates different behavioral effects that depend on signal type. The pattern of results observed for central stimuli are consistent with a model in which neural adaptation is occurring within motor networks encoding movement direction in a distributed manner.

Identity-based inhibitory processing during focused attention

Recent data suggest that the operating principles governing inhibition of distractor-related activity may deviate from dominant models describing inhibitory processing during selective attention. Here we aimed to gain a better understanding of these data in order to determine whether they actually defy premises of current models. In addition to providing evidence against noninhibitory accounts of the data (see especially Experiment 6), the results support three main novel findings that challenge current theories. First, the data provide evidence that inhibition overpowered excitation from ongoing external input (Experiments 1-4), which suggests that inhibitory control processes are more powerful than current models indicate. Second, negative effects emerged even when targets appeared alone (Experiment 5), which suggests that selection does not play an essential role in triggering inhibitory processing. Third, relatively early distractor-related activity was affected, which supports a role for inhibition prior to action control (Experiment 3). These findings suggest a need to revise current models describing inhibition of distracting information during selective attention.

Disorders of higher gaze control

The neural centers in the cerebral hemispheres, both cortex and basal ganglia, involved in the generation of saccadic and smooth pursuit eye movements have been well delineated in terms of their location and function. For the generation of saccades these include the frontal eye fields, the supplementary eye field, and the intraparietal sulcus, and in the basal ganglia the caudate nucleus and the substantia nigra, pars compacta. The generation of pursuit eye movements involves the middle temporal (area V5) and medial superior temporal areas and the frontal eye field. These centers and their connections are disturbed not only in acute and chronic lesions such as cerebral infarction, but also in a wide variety of neurodegenerative diseases. In certain of these conditions, such as patients with cortical dementias and basal ganglia disorders, correct interpretation of the resulting eye movement abnormalities can contribute to differentiating between a range of differential diagnoses.

Evidence for an attentional component in saccadic inhibition of return

After presentation of a peripheral cue, facilitation at the cued location is followed by inhibition of return (IOR). It has been recently proposed that IOR may originate at different processing stages for manual and ocular responses, with manual IOR resulting from inhibited attentional orienting, and ocular IOR resulting form inhibited motor preparation. Contrary to this interpretation, we found an effect of target contrast on saccadic IOR. The effect of contrast decreased with increasing reaction times (RTs) for saccades, but not for manual key-press responses. This may have masked the effect of contrast on IOR with saccades in previous studies (Hunt and Kingstone in J Exp Psychol Hum Percept Perform 29:1068-1074, 2003) because only mean RTs were considered. We also found that background luminance strongly influenced the effects of gap and target contrast on IOR.

Reaction time inhibition from subliminal cues: is it related to inhibition of return?

Task-irrelevant visual cues with near zero visibility proved apt to retard reaction time for the detection of supraliminal visual targets presented at the cued location. The time course of the effect was similar to that of the so-called inhibition-of return (IOR), which is assumed to be due to the withdrawal of attention from the inhibited location. However the present subliminal cues consistently failed to induce an RT facilitation prior to the RT inhibition, contrary to what would be expected if the cue were able to attract attention to the cued location. Since the RT inhibition from subliminal cues could not be attributed to the withdrawal of attention from the cued location, it can be argued that such cues acted both outside of consciousness and without the influence of attention. Therefore, the RT inhibitory effect seems best accounted for by an automatic, unconscious and attention-independent self-inhibition of response tendencies instructed by irrelevant information, akin to that postulated by (Eimer, M., & Schlaghecken, F. (1998). Effects of masked stimuli on motor activation: behavioural and electrophysiological evidence. Journal of Experimental Psychology Human Perception and Performance, 24, 1737-1747.) to explain the negative compatibility effect.

Correlates of Capture of Attention and Inhibition of Return across Stages of Visual Processing

How do visual signals evolve from early to late stages in sensory processing? We explored this question by examining two neural correlates of spatial attention. The capture of attention and inhibition of return refer to the initial advantage and subsequent disadvantage to respond to a visual target that follows an irrelevant visual cue at the same location. In the intermediate layers of the superior colliculus (a region that receives input from late stages in visual processing), both behavioral effects link to changes in the neural representation of the target: strong target-related activity correlates with the capture of attention and weak target-related activity correlates with inhibition of return. Contrasting these correlates with those obtained in the superficial layers (a functionally distinct region that receives input from early stages in visual processing), we show that the target-related activity of neurons in the intermediate layers was the best predictor of orienting behavior, although dramatic changes in the target-related response were observed in both subregions. We describe the important consequences of these findings for understanding the neural basis of the capture of attention and inhibition of return and interpreting changes in neural activity more generally.

Onset but not offset of irrelevant motion disrupts inhibition of return

In seven experiments, subjects were slower to detect targets in cued static objects than in uncued static objects, revealing inhibition of return (IOR). This occurred regardless of the presence or absence of continuous motion of other, task-irrelevant objects in the display. However, if the motion of the irrelevant objects began during the interval between cue and target, the amount of IOR was considerably reduced. Offset of motion during the cue-target interval had no effect. Implications for IOR, object perception, and attentional capture are discussed.