primacy of categorical levels

PRIMACY OF CATEGORY LEVELS

By Guillermo Farfan

Rosch’s prototype theory argues that basic categories should be those which “yield the most information for the least cognitive load” (Rosch, 1976, p.428), i.e. basic objects are the categories for which the cue validity is the highest.

It stands to reason, then, that in terms of primacy, these basic level categories should be processed first. Or do they?

VANRULLEN & THORPE (2001)THE TIME COURSE OF VISUAL PROCESSING

WHAT THEY SET OUT TO DOCurrent theories of visual processing suggest two mechanisms: 1. A perceptual process at the low-end level, and 2. A decision process at the high-end level.

How these mechanisms can be dissociated in time and space was the goal of this study. In addition, VanRullen & Thorpe made the following objections:

• The use of reaction times as a DV make it difficult to separate the respective durations of perception, decision, and motor responses.

• They also noted that the fact that neural activity varies with

respect to the properties of the visual input is not sufficient to conclude that a person is actively recognizing the identity of the category involved.

WHAT WAS THEIR STRATEGY

VanRullen & Tharpe used an alternating dual-task paradigm of event-related potentials (ERPs) to compare the processing of: (1)the same visual category having different

task-related (behavioral) status, and (2)different visual categories having the same

behavioral status. This design allowed them to dissociate low-level sensory activity from high-level task-related mechanism.

WHAT WERE THEIR METHODS

Sample size: 16 subjects 8 men8 womenAges 21-50 yrs old.

Stimuli: Two categorization, release-button tasks (go/no-go) in alternation.Each task consisted of 10 series of 96 images, half targets, half non-targets. Images were flashed for only 20 msec; these include pictures of animals (birds, fish, insects, etc.), or of transport (cars, trains, trucks, etc.)Distractor images were street buildings, fruits, etc.

Data: Using EEGs, event-related potentials were recorded from 32 electrode sites. Electrodes were grouped into frontal, central, parietal, and occipital groups.Intersubject t-tests were conducted at p < .01 for extra precision.There was no difference in performance between tasks.

Differential activity between targets and distractors more marked in the frontal lobe after 150 msec.Despite “transport” being an artificial category, it produces similar electrical responses.Small activity found around 75 msec., but dismissed as changes of the experimental protocol.

Here, the differences in the two visual categories seem to occur after 75-80 msec, and are totally independent of the task and of the status of the images in each task (target and non-target represented equally in each category-specific waveform).

Parietal sides

Grouping of all waveforms from different categories when they were targets vs. all waveforms for same categories when they were non-targets. Here, no differences occur before 150 msec, and are totally independent of the visual category.

Frontal sides

WHAT WERE THEIR RESULTS

VanRullen & Thorpe identified two mechanisms: 1. An early perceptual, task-independent, and category-dependent

process starting at 75-80 msec after stimulus. 2. A later, task-related, category-independent mechanism starting

after 150 msec involving subject’s decision making (target present or not present?) The first is supposedly due to the extraction of visual features happening in extrastriate areas such as V2 or V4.

The second takes place after visual recognition, and the authors suggest that this decision-related activity could be located in occipito-temporal regions.

WHAT WERE THEIR CONCLUSIONSCategorization appears to unfold in two stages:

The behavioral stage,

The perceptual stage, which most likely involves simple visual encoding mechanisms, including the extraction of basic visual properties. which most likely involves the decision made by the subject concerning the object, regardless of the visual category.

Unaware

Aware

ROGERS & PATTERSON (2007)OBJECT CATEGORIZATION

WHAT THEY SET OUT TO DOA paradox exist in literature regarding the process of categorization:1. There’s substantial evidence for Rosch’s idea of basic level

categories, which are intermediate level categories processed faster, and more often, than more general and more specific categories.

2. On the other hand, patients with semantic dementia seem to be better at processing general categories than basic-level or more specific categories, even as the their cognitive system deteriorates.

How to explain this seemingly contradiction was the goal of this study.

WHAT THEY SET OUT TO DO

Rogers & Patterson also examine how spreading-activation models have been used to in the past to account for these differences:

bird node

robin node

animal node

Point of entry

Jolicoeur’s Traditional Model Warrington’s Modified Model

animal node

bird node

robin node

Point of entry

semantic dementia

WHAT THEY SET OUT TO DO

They also argue that Murphy’s differentiation theory falls short because it doesn’t explain why basic-level categories are more susceptible to SD:

bird category robin categoryanimal category

Optimal

semantic dementia ??

Too low Too high


(1)There really is a paradox,(2)That a parallel distributed processing (PDP)

model is better at explaining the phenomena than either spreading- activation and differentiation models, and

(3)That PDP’s predictions can be empirically tested.

VanRullen & Tharpe used three experiments to demonstrate that:

WHAT WERE THEIR METHODSEXPERIMENT 1


Stimuli: 72 color pictures consisting of:Animals and vehicles at the general level; dogs, birds, cars, and boats at the basic level; and Pekinese, Labrador, kingfisher, robin, yacht, ferry, BMW, and Morris at the specific level.Each pic appears once as a target and once as a distractor, for a total of 144 trials.Distractor images were taking from the same 72 pictures.

Data: On each trial, a name would appear, followed by blank screen, and then an onscreen picture until response was detected.Trials were ordered randomly. Reaction times and accuracy were recorded using DMDX software.Repeated-measures ANOVAs and planned comparisons t-tests were used to test for significance.


Faster

More accurate

WHAT WERE THEIR METHODSEXPERIMENT II

Sample size: 8 patients suffering from semantic dementia (SD). 6 men2 womenAges 50-72 yrs old.

Stimuli: Same 72 color pictures used in experiment 1.Each pic was printed, and presented along with the corresponding word, for a total of 144 trials.Distractor images were taking from the same 72 pictures.

Data: On each trial, word + picture would be shown, and the experimenter reads the word aloud. Participants were then asked if the picture matched the word. Pictures were presented semi-randomly. Accuracy was recorded by experimenters. Reaction times were not recorded.Repeated-measures ANOVAs and planned comparisons t-tests were used to test for significance.

WHAT WERE THEIR RESULTSseveremild

There was significant interaction between severity and category level,

F(2, 12)= 8.2, p<.006, = .58

A PARALLEL DISTRIBUTED PROCESSING (PDP) THEORY

Semantic representations are instantiated as distributed patters of neural activity, with different patters corresponding to different concepts.Surface representations capture modality-specific similarity structure, whereas semantic representations capture conceptual similarity structure.Thus, items that are “the same kind of thing” will be represented as similar even if they differ in particulars; items that are “different kinds of things” will be represented as dissimilar even if the share the same characteristics.

cognition

Basic-level categories are distinct and informative, located in tight, widely separated clusters—they are “just right.”

Not distinctive enough

Not informative enough

Not distinctive enough

Not informative enough

Semantic dementia disturbs the activity patters of basic-level and specific categories first before disturbing patterns of general categories.

semantic dementia

Basic-level effects arise as a result of similarity structures coded in the hub, but if conditions are changed (e.g. by SD, or by time pressure), the basic-level advantage would turn into a disadvantage.

In parallelIn normal conditions, animal activates first, but bird reaches full activation before animal or canary does.

WHAT WERE THEIR METHODSEXPERIMENT III


Stimuli: 72 color pictures consisting same as experiment 1.Each pic appears once as a target and once as a distractor, for a total of 144 trials.Distractor images were taking from the same 72 pictures.

Data: Same as experiment I, but responses were timed with a deadline.All stimuli and conditions from experiment I were repeated at three different deadlines: slow, medium, and fast.Repeated-measures ANOVAs and planned comparisons t-tests were used to test for significance.

Responses that did not meet the deadline of 100 ms were discarded (21% of all trials).

53% of trials were further discarded for this analysis.

WHAT WERE THEIR CONCLUSIONS PDP predicted that, when pressed for time,

participants’ responses would resemble SD patients because decisions about category membership were impaired—by neural degradation, in SD case, and by not enough activation time, in the time-pressure case.

In many theories, the goal of the recognition process is the activation of entry-level (basic) categories, with little attention paid to general categories, since they’re assumed to be “semantic” and usually independent.

Rogers & Patterson argue, instead, that more general levels are processed first, even if full activation does not occur after basic-level categories are recognized.

Finally, the authors note that the separation of perceptual categorization and semantic processing is wrong as they’re both parts of the same interactive system, and that PDP avoids the difficult challenges associated with feature-based prototype theories.

MACK & PALMERI (2015)THE DYNAMICS OF CATEGORIZATION

WHAT THEY SET OUT TO DOLike the previous article, Mack & Palmeri wanted to explain away the contradiction between basic-level categories having an advantage during speeded category trials, and superordinate categories having an advantage during ultrarapid categorization trials.

In particular, Mack & Palmeri wanted to address the following methodological factors:

• The exposure duration of the stimulus during speeded categorization (longer) vs. ultrarapid categorization (very short).

• The local context and structure of each type of trial, as

speeded categorization usually employs randomized design, whereas ultrarapid uses blocked design, in addition to the possibility of priming after repetition.


(1)A conjunction of both brief exposure and blocked target category context are necessary to see a superordinate advantage (experiment 1).

(2)Exposure duration has an effect when targets are blocked (experiments 2-3).

(3)Target category context has an effect when exposures are brief (experiments 4-5).

Mack & Palmeri used five (!) experiments to show that:

WHAT WERE THEIR METHODSEXPERIMENT 1

Sample size: 56 students 21 men35 womenAges 18-23 yrs old.

Stimuli: Several images of:Most popular dog breeds (e.g. beagle, Labrador, etc.), backyard birds (e.g. blue jay, American robin, etc.), many species of flowers, and trees.No stimulus image was repeated during an experimental session.

Data: Exposure duration (25 ms or 250 ms) and target context (randomized or blocked) were fully crossed to create 4 conditions.Participants were randomly assigned to one of these conditions. Trials were presented in 36 trials sets, for a total of 228 trials (including 12 practice trials). One-way ANOVAs and planned comparisons t-tests were used to test for significance.


With long exposures, a basic-level advantage in RT, sensitivity, or both was observed regardless of whether the target category was blocked or randomized

short long short long

This advantage vanishes with short exposure + blocked target category, the two features of ultrarapid categorization.Brief exposure, then, is critical to eliminate basic-level advantage, but only when categorizing at a particular level of abstraction.

WHAT WERE THEIR METHODSEXPERIMENT 1I


Stimuli: Several images of dogs, animals, and means of transportation.Dog images include the ones use for experiment 1, plus some more; animals came from a variety of other species, in addition to many categories of transportation. No stimulus image was repeated during an experimental session.

Data: Participants performed a category verification task at either the superordinate or basic level. Target category was blocked; half of the trials were “yes” (half of these were dogs), the other half were “no” (means of transportation were randomly chosen for the “no” trials). Exposure varied at six intervals, from 25 to 250 ms.Participants completed 624 trials in total (52 trials in each of the 12 conditions). A 2x6 ANOVA and planned comparisons tests were used to test for significance.


There was a significant main effect of exposure duration, F(5, 115)= 48.37, p<.001, = .028, but no significant main effect of category level.There was a significant interaction between the two factors: with short exposure, sensitivity was higher in superordinate categories. However, with longer exposure the situation reverses, with basic-level categories having higher sensitivity.(shot out to Rogers & Patterson)

WHAT WERE THEIR METHODSEXPERIMENT III

Sample size: 14 students 6 men 8 womenAges 18-24 yrs old.

Stimuli: Same stimuli as experiment II.No stimulus image was repeated during an experimental session.

Data: Same procedure as experiment II, with the exception of:Stimulus image appear constantly for 25ms, followed by a dynamic mask at five varied intervals, from 25 to 125 ms.Participants completed six blocks, 3 with the superordinate animal, and 3 with the basic-level dog, for a total of 600 trials (60 trials in each of the 10 conditions). A 2x5 ANOVA and planned comparisons tests were used to test for significance.

WHAT WERE THEIR RESULTSThe extent to which categorization is resilient to the onset of the mask reveals how much category relevant information is available at that point in time. Results suggest that, with brief exposures, the information relevant for category decisions favors superordinate over basic category. That is, this superordinate information is available quickly, and is of better quality initially.

(again, shot out to Rogers & Patterson)

ULTRARAPID VS SPEEDED TRIALS

Aside from differences in exposure duration, which we have seen, do these other

procedural differences matter?

Blocked design

Participants aware of target category

Decision criteria optimized for fastest responses

Random design

Participants unaware of target category

Stimulus exposure is unlimited

Lots of practice trials Very few (or none) practice trials

WHAT WERE THEIR METHODSEXPERIMENT 1V


Data: Same as experiment 1, with the exception of:All stimuli was presented briefly (25 ms); half of the experiment used blocked target category, and the other half used randomized target category. Stimuli were randomly assigned to the either blocked or randomized category contexts. There was a filler task of aprox. 30 min. in between.A 2x3 ANOVA and planned comparisons tests were used to test for significance.

Stimuli: Same images as experiment 1:Most popular dog breeds (e.g. beagle, Labrador, etc.), backyard birds (e.g. blue jay, American robin, etc.), many species of flowers, and trees.No stimulus image was repeated during an experimental session.

WHAT WERE THEIR RESULTSA basic-level advantage is shown in the randomized context, but the RT advantage disappears in the blocked context.Blocked target context might be given participants an opportunity to increase efficiency (but not accuracy) in all category levels.

WHAT WERE THEIR METHODSEXPERIMENT V


Stimuli: Same as experiment II, plus birds from experiment I.No stimulus image was repeated during an experimental session.

Data: Participants performed the same category verification task as in previous ultrarapid trials.Trails were critical pairs (one of four types, depending on same/ different level of abstraction), baseline pairs (an unrelated parity task, followed by a superordinate-basic level prime), and filler pairs (an unrelated parity task followed by nonmatching categories).Participants completed 472 (including 12 practice trials). A 2x2x2 ANOVA and planned comparisons tests were used to test for significance.

WHAT WERE THEIR RESULTSOn average, basic-level categorization is faster than superordinate categorization, in both baseline and prime trials. It is also robust to local variation in experimental context.Conversely, superordinate categorization is significantly affected by the type of prime.This is consistent with a spreading activation account.

WHAT WERE THEIR RESULTSThis graph shows that the basic-level advantage in RT is eliminated after only 4 trials of superordinate categorization.The increase in superordinate RT could be due to a transition from mediated processing through semantic knowledge to more direct perceptual retrieval in episodic memory.This increase in RT efficiency is only available for a limited window of time.

WHAT WERE THEIR CONCLUSIONSMack & Palmeri make the following observations:

A common theoretical position is that certain levels of abstraction are faster, better, and first because they’re primary in some way by access, logic, and/or development.

Neither exposure duration (time course) nor local categorization context alone is sufficient to explain the speed of categorization at different levels of abstraction. Rather, it’s the interaction between these two that determines when categorization at one level would be faster than at another level.

In a default state, basic-level categories have an advantage during visual categorization. However, under very specific conditions, superordinate categorization can be as fast if not faster than basic-level categorization after a very short time.

FINAL THOUGHTS

Why is superordinate categorization

sensitive to target category context when basic-level categorization is

not?

primacy of categorical levels

Education