afterimage is the image that remains after a stimulus is removed.
afterimage is the image that remains after a stimulus is removed.
the image that remains after a stimulus is removed?
afterimage
formed image perseveration refers to a single, stationary object that remains fixed in one's visual field. these pathological afterimages look realistic and have the same color and clarity as the original stimulus. the palinopsia lasts at least 15 seconds, but may persist for hours or days. for example, a patient sees a cat, and an identical copy of the cat remains fixed in the field of view for 30 minutes. a patient commonly complains of the perseverated fingers of an examiner. these afterimages often occur in visual field deficits but may occur anywhere in the visual field, regardless of the location of the original stimulus. the generation of the afterimages is not affected by external conditions such as the length of fixation, stimulus intensity, contrast, or motion. the palinoptic image can appear immediately after seeing the original image or may be delayed in time.
hallucinatory palinopsia
ray "skip" johnson, jr., now a professor at queens college, published a triarchic model of p300 amplitude in 1986. although he does not explicitly refer to p3b in this paper, most of his discussions refer to p3b. he offered three things that affected the amplitude – subjective probability, stimulus meaning, and information transmission. he summarized his view in the following formula: p300 amplitude = f[t x (1/p + m)], where p is subjective probability, m is stimulus meaning, and t is information transmitted. he describes subjective probability as objective probability with the added element of human judgment of how relevant a stimulus is to the task, and notes that p300 amplitude is directly related to the amount of uncertainty that is reduced by a stimulus. however, it has also been found that p300 amplitude can change in the absence of changes in probability. stimulus meaning therefore refers to variables that account for the processing of a stimulus that are not related to probability. (recall that chapman and bragdon found that only the stimulus that had meaning in their experiment elicited the late positivity.) stimulus meaning encompasses three independent variables that can be manipulated – task complexity (how difficult a task is, or how many tasks must be performed at once), stimulus complexity (perceptual demand, or how many relevant features of the stimulus must be processed – a face being more complex than a dot), and stimulus value (the significance, or for example the monetary value: the greater the value the larger the p300 amplitude). information transmission is the proportion of stimulus information received by a person relative to how much information the stimulus originally contained. there are external and internal manipulations of information transmission. when much information is lost for external reasons, for example because the stimulus is harder to discriminate or perceive, p300 amplitude is lower. internal manipulations are variations in how much attention subjects are required or allowed to give to the stimulus. p3b requires attention, and increasing the difficulty of maintaining attention will correspondingly decrease p3b amplitude. to summarize, johnson describes that probability on many levels, the relevance of the stimulus to the task, and the amount information a stimulus transmits are all variables that will determine p3b amplitude.
p3b