title: A behavioural perspective of visual search and the low prevalence effect

authors: Hollands, David M.

abstract: In visual search, rare items are missed disproportionately often. This Low Prevalence Effect (LPE) is a robust phenomenon with important societal consequences. We asked the question, “Is the schedule of signal presentation controlling eye movements and if so, how?” and hypothesised that visual search is an operant behaviour. To answer this question, we examined the LPE using eye-tracking and incorporated a rich schedule of signal presentation (medium-prevalence condition: 0.50 target probability across 200 trials) and a lean schedule (low-prevalence condition: 0.02 or 0.00 target probability across 1,000 trials) over three experiments. Experiment One was the control, in Experiments Two and Three we increased task difficulty by incorporating a staircase titration procedure, and in Experiment Three we also removed all target-present trials in the low-prevalence condition. We replicated the LPE in all experiments and observed increased levels of searching eye movements throughout the medium-prevalence condition due to an increase in behaviour for the first correct rejection immediately following a correct target-present response which we attribute to the local effects of reinforcement and the strengthening of search behaviour when we find what we are looking for. We also observed that visual attention was being guided towards the densest population of stimulus items (centroid) at the beginning of their search as a search strategy and conclude that this centroid zone is acting as a discriminative stimulus signalling the availability of reinforcement. We contend that eye movements are an operant behaviour controlled by environmental contingencies and reinforcement mechanisms are behind the LPE phenomenon.

text: A behavioural perspective of visual search and the low prevalence effect In visual search, rare items are missed disproportionately often. This Low Prevalence Effect (LPE) is a robust phenomenon with important societal consequences. We asked the question, “Is the schedule of signal presentation controlling eye movements and if so, how?” and hypothesised that visual search is an operant behaviour. To answer this question, we examined the LPE using eye-tracking and incorporated a rich schedule of signal presentation (medium-prevalence condition: 0.50 target probability across 200 trials) and a lean schedule (low-prevalence condition: 0.02 or 0.00 target probability across 1,000 trials) over three experiments. Experiment One was the control, in Experiments Two and Three we increased task difficulty by incorporating a staircase titration procedure, and in Experiment Three we also removed all target-present trials in the low-prevalence condition. We replicated the LPE in all experiments and observed increased levels of searching eye movements throughout the medium-prevalence condition due to an increase in behaviour for the first correct rejection immediately following a correct target-present response which we attribute to the local effects of reinforcement and the strengthening of search behaviour when we find what we are looking for. We also observed that visual attention was being guided towards the densest population of stimulus items (centroid) at the beginning of their search as a search strategy and conclude that this centroid zone is acting as a discriminative stimulus signalling the availability of reinforcement. We contend that eye movements are an operant behaviour controlled by environmental contingencies and reinforcement mechanisms are behind the LPE phenomenon.

year: 2024

title: Vectorised SIMD Implementations of Morphology Algorithms

authors: Cree, Michael J.

abstract: We explore vectorised implementations, exploiting single instruction multiple data (SIMD) CPU instructions on commonly used architectures, of three efficient algorithms for morphological dilation and erosion. We discuss issues specific to SIMD implementation and describe how they guide algorithm choice. We compare our implementations to a commonly used opensource SIMD accelerated machine vision library and find orders of magnitude speed-ups can be achieved for erosions using two-dimensional structuring elements.

text: Vectorised SIMD Implementations of Morphology Algorithms We explore vectorised implementations, exploiting single instruction multiple data (SIMD) CPU instructions on commonly used architectures, of three efficient algorithms for morphological dilation and erosion. We discuss issues specific to SIMD implementation and describe how they guide algorithm choice. We compare our implementations to a commonly used opensource SIMD accelerated machine vision library and find orders of magnitude speed-ups can be achieved for erosions using two-dimensional structuring elements.

year: 2015

title: Perception and flagging of loanwords – A diachronic case-study of Māori loanwords in New Zealand English

authors: Levendis, Katharine

abstract: This paper combines a quantitative and qualitative analysis of a diachronic corpus of New Zealand newspapers built to analyse the use of Māori loanwords in New Zealand English. We report findings in relation to flagging (marking of loanwords as being foreign material in a given language) and show that it is (weakly) predicated by frequency-of-use and by semantic category of the loanword (core loans are flagged more than cultural ones), but not by listedness. Alongside this trend, we note that perceptions of writers using the words vary enormously in regard to which loans are integrated and familiar, matching neither listedness nor frequency-of-use patterns. This indicates that in NZE, loanword use remains strongly tied up with socio-political identity and language ideology, rather than rooted in linguistic factors (such as, bilingualism or filling in lexical gaps).

text: Perception and flagging of loanwords – A diachronic case-study of Māori loanwords in New Zealand English This paper combines a quantitative and qualitative analysis of a diachronic corpus of New Zealand newspapers built to analyse the use of Māori loanwords in New Zealand English. We report findings in relation to flagging (marking of loanwords as being foreign material in a given language) and show that it is (weakly) predicated by frequency-of-use and by semantic category of the loanword (core loans are flagged more than cultural ones), but not by listedness. Alongside this trend, we note that perceptions of writers using the words vary enormously in regard to which loans are integrated and familiar, matching neither listedness nor frequency-of-use patterns. This indicates that in NZE, loanword use remains strongly tied up with socio-political identity and language ideology, rather than rooted in linguistic factors (such as, bilingualism or filling in lexical gaps).

year: 2019