Competitive mechanisms subserve attention in macaque areas V2 and V4.
It is well established that attention modulates visual processing in extrastriate cortex. However, the underlying neural mechanisms are unknown. A consistent observation is that attention has its greatest impact on neuronal responses when multiple stimuli appear together within a cell's receptive field. One way to explain this is to assume that multiple stimuli activate competing populations of neurons and that attention biases this competition in favor of the attended stimulus. In the absence of competing stimuli, there is no competition to be resolved. Accordingly, attention has a more limited effect on the neuronal response to a single stimulus. To test this interpretation, we measured the responses of neurons in macaque areas V2 and V4 using a behavioral paradigm that allowed us to isolate automatic sensory processing mechanisms from attentional effects. First, we measured each cell's response to a single stimulus presented alone inside the receptive field or paired with a second receptive field stimulus, while the monkey attended to a location outside the receptive field. Adding the second stimulus typically caused the neuron's response to move toward the response that was elicited by the second stimulus alone. Then, we directed the monkey's attention to one element of the pair. This drove the neuron's response toward the response elicited when the attended stimulus appeared alone. These findings are consistent with the idea that attention biases competitive interactions among neurons, causing them to respond primarily to the attended stimulus. A quantitative neural model of attention is proposed to account for these results. (+info)
An analysis of multiple misplaced parental social contingencies.
This study analyzed the training of a mother to modify five subclasses of her attention to her young child's noncompliance with instructions, and also displayed the changes in her child's behavior correlated with these events. Training in four subclasses consisted of teaching the mother to withhold various forms of social attention to her daughter's undesired behavior; training in the fifth subclass involved introduction of a brief room-timeout procedure for noncompliance. The effectiveness of the parent-training procedure, consisting of initial instructions and daily feedback, was demonstrated through a multiple-baseline design across the five subclasses of parent behavior. Sequential decreased in the first three subclasses of the mother's social attention to undesired child behavior resulted in incomplete improvements in some child responses; however, a decrease in the fourth subclass resulted in a significant increase in undesired child behavior. Complete remediation of all child behaviors was achieved following the training of a timeout procedure for noncompliance. Postchecks conducted up to 16 weeks later showed that these effects were durable. (+info)
Blocking a selective association in pigeons.
Experiment 1 demonstrated for the first time a stimulus-reinforcer interaction in pigeons trained with free-operant multiple schedules of reinforcement. Pigeons that treadle pressed in the presence of a tone-light (TL) compound for food exhibited primarily visual stimulus control on a stimulus-element test, whereas pigeons that avoided shock in TL exhibited auditory control. In Experiment 2, this selective association was blocked in pigeons pretrained with the biologically contingency-disadvantage element of the compound (i.e., tone-food or light-shock) before TL training. When this pretraining preceded compound-stimulus training, control was now auditory in pigeons that treadle pressed for food and was visual in pigeons that avoided shock. Previous attempts at blocking this selective association were unsuccessful in pigeons (LoLordo, Jacobs, & Foree, 1982) but were successful in rats (Schindler & Weiss, 1985). Experiment 2 established that selective associations can be blocked in pigeons when the procedures that were effective with rats were systematically replicated. These results further demonstrate the cross-species generality of an associative attentional mechanism involving a biological constraint on learning in species with different dominant sensory systems. (+info)
The cerebral haemodynamics of music perception. A transcranial Doppler sonography study.
The perception of music has been investigated by several neurophysiological and neuroimaging methods. Results from these studies suggest a right hemisphere dominance for non-musicians and a possible left hemisphere dominance for musicians. However, inconsistent results have been obtained, and not all variables have been controlled by the different methods. We performed a study with functional transcranial Doppler sonography (fTCD) of the middle cerebral artery to evaluate changes in cerebral blood flow velocity (CBFV) during different periods of music perception. Twenty-four healthy right-handed subjects were enrolled and examined during rest and during listening to periods of music with predominant language, rhythm and harmony content. The gender, musical experience and mode of listening of the subjects were chosen as independent factors; the type of music was included as the variable in repeated measurements. We observed a significant increase of CBFV in the right hemisphere in non-musicians during harmony perception but not during rhythm perception; this effect was more pronounced in females. Language perception was lateralized to the left hemisphere in all subject groups. Musicians showed increased CBFV values in the left hemisphere which were independent of the type of stimulus, and background listeners showed increased CBFV values during harmony perception in the right hemisphere which were independent of their musical experience. The time taken to reach the peak of CBFV was significantly longer in non-musicians when compared with musicians during rhythm and harmony perception. Pulse rates were significantly decreased in non-musicians during harmony perception, probably due to a specific relaxation effect in this subgroup. The resistance index did not show any significant differences, suggesting only regional changes of small resistance vessels but not of large arteries. Our fTCD study confirms previous findings of right hemisphere lateralization for harmony perception in non-musicians. In addition, we showed that this effect is more pronounced in female subjects and in background listeners and that the lateralization is delayed in non-musicians compared with musicians for the perception of rhythm and harmony stimuli. Our data suggest that musicians and non-musicians have different strategies to lateralize musical stimuli, with a delayed but marked right hemisphere lateralization during harmony perception in non-musicians and an attentive mode of listening contributing to a left hemisphere lateralization in musicians. (+info)
Unilateral neglect and disambiguation of the Necker cube.
Three groups of patients (right brain-damaged patients with or without left neglect, and left brain-damaged patients) and a group of healthy subjects, matched for age and educational level to the three groups of patients, were asked to report which of the two frontal surfaces of Necker cubes oriented in four different ways looked, at first sight, nearer to the viewer. The extent to which, and the way in which, disambiguation of the apparent perspective of Necker cubes occurred was found to vary across the four orientations and to be different in left-neglect patients compared with subjects of the other three groups. With normal subjects, the disambiguating factor is suggested to be a disposition to perceive the upper surface, which is nearly orthogonal to the frontal plane, as external to the cube. This would result from a navigation of the observer's spatial attention towards its target along a particular path that is altered in patients suffering from left neglect. It is suggested that comparison of the paths followed by the attentional vectors of normal subjects and left-neglect patients is potentially fruitful for a better understanding of the brain's normal mechanisms of spatial attention and of unresolved issues concerning the perception of the Necker cube. (+info)
Impairment in preattentive visual processing in patients with Parkinson's disease.
We explored the possibility of whether preattentive visual processing is impaired in Parkinson's disease. With this aim, visual discrimination thresholds for orientation texture stimuli were determined in two separate measurement sessions in 16 patients with idiopathic Parkinson's disease. The results were compared with those of 16 control subjects age-matched and 16 young healthy volunteers. Discrimination thresholds were measured in a four-alternative spatial forced-choice paradigm, in which subjects judged the location of a target embedded in a background of distractors. Four different stimulus configurations were employed: (i) a group of vertical targets among horizontal distractors ('vertical line targets'); (ii) targets with varying levels of orientation difference on a background of spatially filtered vertically oriented noise ('Gaussian filtered noise'); (iii) one 'L' among 43 '+' signs ('texton'), all of which assess preattentive visual processing; and (iv) control condition, of one 'L' among 43 'T' distractors ('non-texton' search target), which reflects attentive visual processing. In two of the preattentive tasks (filtered noise and texton), patients with Parkinson's disease required significantly greater orientation differences and longer stimulus durations, respectively. In contrast, their performance in the vertical line target and non-texton search target was comparable to that of the matched control subjects. These differences were more pronounced in the first compared with the second session. Duration of illness and age within the patient group correlated significantly with test performance. In all conditions tested, the young control subjects performed significantly better than the more elderly control group, further indicating an effect of age on this form of visual processing. The results suggest that, in addition to the well documented impairment in retinal processing, idiopathic Parkinson's disease is associated with a deficit in preattentive cortical visual processing. (+info)
Spatial attention affects brain activity in human primary visual cortex.
Functional MRI was used to test whether instructing subjects to attend to one or another location in a visual scene would affect neural activity in human primary visual cortex. Stimuli were moving gratings restricted to a pair of peripheral, circular apertures, positioned to the right and to the left of a central fixation point. Subjects were trained to perform a motion discrimination task, attending (without moving their eyes) at any moment to one of the two stimulus apertures. Functional MRI responses were recorded while subjects were cued to alternate their attention between the two apertures. Primary visual cortex responses in each hemisphere modulated with the alternation of the cue; responses were greater when the subject attended to the stimuli in the contralateral hemifield. The attentional modulation of the brain activity was about 25% of that evoked by alternating the stimulus with a uniform field. (+info)
Attentional ability among survivors of leukaemia.
Attentional ability in 19 survivors of acute lymphoblastic leukaemia and 19 sibling controls was assessed using a neuropsychological model of attention. Analysis revealed that children who had received treatment for leukaemia exhibited significantly poorer performance on measures of the "focus encode" and "focus execute" elements of attention and on measures of the ability to respond to external cues and feedback. No significant differences in performance were found for measures of sustained attention and the ability to shift attention. These results indicate that children who have received treatment for leukaemia may experience highly specific attentional deficits that could have an impact on academic performance, particularly mathematical and reading skills. It is suggested that this underlying attentional deficit might be the source of the neuropsychological sequelae associated with the disease. Future attempts at remediation should incorporate activities specifically designed to ameliorate focusing difficulties. (+info)