stimuli, even though fairly weak, may also generate response occasionally by slipping through the selective filter. Multimode theory was developed by Johnston and Heinz ( ). This theory believes that attention is a flexible system that allows selection of a stimulus over others at three stages. At stage one the sensory representations (e.g., visual images) of stimuli are constructed; at stage two the semantic representations (e.g., names of objects) are constructed; and at stage three the sensory and semantic representations enter the consciousness.
It is also suggested that more processing requires more mental effort. When the messages are selected on the basis of stage one processing (early selection), less mental effort is required than when the selection is based on stage three pr ocessing (late selection). Sustained Attention While selective attention is mainly concerned with the selection of stimuli, sustained attention is concerned with concentration. It Our attention has a limited capacity to receive stimuli.
The number of objects one can attend to at a brief exposure (i.e. a fraction of a second) is called “span of attention” or “perceptual span”. More specifically, the span of attention refers to the amount of information an observer can grasp from a complex array of stimuli at a single momentary exposure. This can be determined by the use of an instrument, called “tachistoscope”.
On the basis of several experiments, Miller has reported that our .