Search PubMed⌕ Search

Biomedical subjects

S F Sands

Publications and source records attributed to S F Sands.

13 recordsLinked to original sources
PubMed1992

Attentional cues in chronic schizophrenia: abnormal disengagement of attention.

Posner's (1980) reaction time (RT) paradigm was used to examine the engagement and disengagement operations of visual selective attention in patients with schizophrenia. In the 1st experiment, 14 medicated, chronic schizophrenic subjects (diagnosed by criteria of the Diagnostic and Statistical Manual of Mental Disorders; American Psychiatric Association, 1987) and 15 age-matched normal control subjects made a speeded response to a target preceded by a valid, an invalid, or no cue. Control subjects showed the expected advantage and disadvantage in RT for valid and invalid cues, which suggests intact engagement and disengagement operations. For schizophrenic patients, valid cues also enhanced RT, but invalid cues did not slow RT. Similar results were found in the 2nd experiment. The failure of unpredictable, invalid cues to inhibit RT in chronic schizophrenia may be related to an abnormality in the disengagement operation of selective attention.

Adult↗
PubMed1991

Neuroleptics improve sustained attention in schizophrenia. A study using signal detection theory.

To test the hypothesis that antipsychotic drugs improve attentional processes in schizophrenia, we used a computer-controlled, perceptually degraded continuous performance test (CPT), based on signal detection theory. CPT stimuli were degraded (blurred) to reduce discriminability so that signal detection analysis could be used to distinguish specific attentional processes, as measured by A', from nonspecific factors, as measured by B". Thirteen medicated and 12 neuroleptic-withdrawn schizophrenics visually monitored digits to detect a target under perceptually undegraded and degraded conditions. The principal result was that the neuroleptic-withdrawn patients showed a significant decline in the attention-specific measure of A' over time on task only for the degraded targets, independent of changes in the nonspecific index of B". These results demonstrate that neuroleptic withdrawal may compromise specific attentional processes, namely the ability to sustain attention, as measured by a precise performance task which controlled for nonspecific factors.

Adult↗
PubMed1985

Memory processing of serial lists by pigeons, monkeys, and people.

List memory of pigeons, monkeys, and humans was tested with lists of four visual items (travel slides for animals and kaleidoscope patterns for humans). Retention interval increases for list-item memory revealed a consistent modification of the serial-position function shape: a monotonically increasing function at the shortest interval, a U-shaped function at intermediate intervals, and a monotonically decreasing function at the longest interval. The time course of these changes was fastest for pigeons, intermediate for monkeys, and slowest for humans.

Adult↗
PubMed1984

Monkey memory: same/different concept learning, serial probe acquisition, and probe delay effects.

Three rhesus monkeys were trained and tested in a same/different task with six successive sets of 70 item pairs to an 88% accuracy on each set. Their poor initial transfer performance (55% correct) with novel stimuli improved dramatically to 85% correct following daily item changes in the training stimuli. They acquired a serial-probe-recognition (SPR) task with variable (1-6) item list lengths. This SPR acquisition, although gradual, was more rapid for the monkeys than for pigeons similarly trained. Testing with a fixed list length of four items at different delays between the last list item and the probe test item revealed changes in the serial-position function: a recency effect (last items remembered well) for 0-s delay, recency and primacy effects (first and last list items remembered well) for 1-, 2-, and 10-s delays, and only a primacy effect for the longest 30-s delay. These results are compared with similar ones from pigeons and are discussed in relation to theories of memory processing.

Animals↗
PubMed1982

Monkey and human pictorial memory scanning.

A rhesus monkey accurately recognized pictures in a Sternberg memory scanning experiment. When the monkey was tested with pictures that were reused during the same session, the monkey's performance was nearly identical to that of a human subject; this result demonstrates the monkeys are capable of some of the short-term retrieval mechanisms of humans.

Adult↗
PubMed1982

Pictorial similarity judgments and the organization of visual memory in the rhesus monkey.

The organization of visual memory for pictures was studied in the rhesus monkey. Two monkeys were tested in a same/different task in which sequentially presented pictures were compared to each other in a pair-wise fashion. The resulting confusion matrixes were analyzed using a multidimensional scaling procedure to obtain two- and three-dimensional graphic representations of the stimulus space. In Experiment 1, the monkeys' confusion errors caused pictures of human and rhesus monkey faces to fall in the same region of multidimensional space, which suggested that the monkeys categorized facial stimuli. A similar effect was found for pictures of different types of fruit. Experiment 2 replicated the categorization of faces with a more diverse collection of human and nonhuman primate faces. Experiment 3 explored the fruit category by varying stimulus attributes orthogonally. The results from this experiment showed that both monkeys encoded the pictures in this category by type of fruit (apples or grapes) and color (red or yellow). Taken together, these studies indicate that rhesus monkeys will treat some classes of pictorial stimuli categorically in visual memory.

Animals↗
PubMed1980

Primate memory: retention of serial list items by a rhesus monkey.

A rhesus monkey correctly recognized 86 and 81 percent of 10- and 20-item lists, respectively. It serial position curve was similar in form to a human's curve, revealing prominent primacy and recency effects. The key to these findings was in minimizing proactive interference through the use of a large pool of 211 color photographs.

Adult↗
PubMed1980

Serial probe recognition performance by a rhesus monkey and a human with 10- and 20-item lists.

A rhesus monkey performed at high accuracy in a serial probe recognition task with color pictures as stimuli. The monkey's serial position curve was similar in form to a human's and demonstrated the theoretically important primacy and recency effects with lists containing as many as 10 or 20 items. The high accuracy of the monkey was shown to be largely due to the minimization of proactive interference through the use of more than 200 distinct items. These results encourage the view of similar mechanisms of memory in monkey and humans.

Animals↗
PubMedDate not supplied

Measurement of visual sustained attention in schizophrenia using signal detection analysis and a newly developed computerized CPT task.

Sustained attention in schizophrenia was assessed with a newly developed, computer-controlled, modified version of the continuous performance test in which specific attentional effects can be empirically distinguished from nonspecific factors by signal detection theory (SDT). Results indicated that patients showed a more rapid decline in specific attentional, but not nonspecific processes, as measured by SDT parameters of A' and B", respectively.

Adult↗
PubMedDate not supplied

Fat within the falx: MR demonstration of falcine bony metaplasia with marrow formation.

Falcine bony metaplasia frequently is incorrectly labeled "dense calcification" on brain CT and conventional radiography. Of 3,000 brain magnetic resonance (MR) scans reviewed, 12 demonstrated a central area of increased signal intensity on T1 and T2 weighted images with a smooth peripheral rim of diminished signal intensity within the region of the falx. The central area of increased signal intensity corresponded to fat in the medullary cavity and the peripheral area of low signal intensity corresponded to cortical bone. The CT scans, available in nine of 12 patients, were compared with the MR scans and revealed dense mineralization in the corresponding region of the falx. A postmortem specimen of densely "calcified" falx cerebri was examined that revealed cortical bone and a medullary cavity complete with bony trabeculae and marrow. The MR findings of falx ossification should not be confused with other entities of greater clinical significance.

Adipose Tissue↗
PubMedDate not supplied

Giant cranial hemangiopericytoma: MR and angiographic findings.

The authors detail the MR and angiographic findings of a very large hemangiopericytoma in the skull of a 63-year-old woman. Angiography showed a marked tumor blush with early draining veins; MR showed heterogeneously increased T2 signal intensity and enhancement with gadolinium secondary to the richly vascularized tumor.

Angiography↗